You can actually rent.
Wether it's on a private sim or in mainland. The hardest thing is to find a good land owner, actually. Even if you "buy" (it's like a rental) on a private sim.
I've been renting houses in SL since 2007. I rent not only the house, but the parcel that surrounds it. Usually, I do that in mainland, in my properties close to LL ocean, where nobody can cover your view and you can have a good use of the water amenities - sail etc.
For that, you don't need to have a premium account (neither does your friend), because you pay the land owner and not LL. (private sim or mainland)
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Saphyrial Sella
Nightingale's Estates Administration
www.nightingalesestates.blogspot.com