... owned this property only as a "leasehold" (the approximate equivalent of property entered in the land register as "easement" under Swiss law)

Baurecht
1) Befugnis auf einem fremden Grundstück ein Bauwerk zu errichten.
2) Summe der Rechtsnormen zur Regelung der Bautätigkeit (öffentliches B.).

http://www.hev-schweiz.ch/Dienstleistungen/immo_lexikon.htm

Boden im Baurecht erwerben?
Das als Dienstbarkeit im Grundbuch einzutragende Baurecht erlaubt Ihnen als Baurechtnehmer, auf einem fremden Grundstück ein Gebäude zu erstellen und es als Eigentümer zu nutzen. Nach Ablauf des Baurechts fällt das erstellte Gebäude an den Baurechtgeber zurück (Heimfall). Hierfür zahlt dieser Ihnen als bisherigen Baurechtnehmer eine angemessene Entschädigung, die sogenannte Heimfall-Entschädigung. Deren Höhe, aber auch weitere Pflichten, wie etwa die Wiederherstellung des ursprünglichen Zustandes (d.h. Abbruch des Gebäudes), wird im Baurechtsvertrag vereinbart. Vor der Unterzeichnung eines Baurechtsvertrags sollten Sie sich also unbedingt von einem Experten beraten lassen.

Buying the Right to Build on a Plot of Land
If you purchase building rights which are entered in the land register as "easement" you are permitted to erect a building on a plot of land which you do not own and use that building as its owner. When the building rights expire the building which has been erected becomes the property of the person who granted the building rights (reversion). In return, the latter pays the former holder of the building rights suitable compensation, known as reversion payment. The amount of this compensation is stipulated in the building rights agreement, as are other provisions such as returning the plot to its original condition (i.e. demolishing the building). You should, therefore, seek the advice of an expert before you sign a building rights

https://entry.credit-suisse.ch/csfs/p/rb/en/hypo/recht/rct_b...

Real Estate in Switzerland

Servitudes and Easements

c) Right to Build
A right to build (Baurecht/droit de superficie)
entitles the beneficiary to construct buildings on the property in accordance with an agreement between the parties and to possess and enjoy it for a definite period of time, which may be up to 100 years. The right is – in the absence of a contrary agreement – transferable and inheritable.
Any agreement which establishes a right to build must be in writing
and notarized. Upon expiration of the term, any existing buildings
belong to the owner, who is obliged to pay the beneficiary a reasonable price for those buildings. The parties may (and mostly do) agree on a method of determining that price when they establish the right to build. The right to build has gained significance in recent years as an increasing number of communities have used it as a means of offering undeveloped land under favorable conditions to the public for the construction of residential housing or to start new businesses. The fact that the land was not sold but only a right to build, granted usually for 99 years, gave the communities the right to exercise greater influence on the character of the construction projects than if they had sold it. In addition, there is a strong policy argument made against the irrevocable sale of publicly owned land to private entities.

http://www.baerkarrer.ch/Publications/1004/4_3_5.pdf

An interesting option is to register specific rights in the Land Register. These can be easements (like rights of way or specific obligations) or – very important in practice – independent and permanent rights of building. When a right of building is established, ownership of the soil and the building can be split. The owner of the soil establishes a servitude on the soil so that every subsequent owner of the soil is bound by the agreement establishing the right of building. After the end of the agreement, the ownership of the building reverts to the owner of the soil, but he has to reimburse the remaining value of the buildings.

http://www.nexia.ch/_library/pdf/Nexia_Real_EstateBroschure_...

is my suggestion for the whole phrase, if you need to make clear that this explanation appears in the original document. Otherwise I would just leave it out :-)