First you need to download
Quake 2 VRmod[github.com]
unpack it and test it.

Rename the baseq2 folder to what ever you want. (baseq2.org for example)
Go to your "thirty flights of loving" folder.
Copy "zlib.dll", "libpng.dll" and the baseq2 folder to your Quake2-Rift folder.
Copy everything from your baseq2.org (or what ever you named it) to the new baseq2 folder.
OVERWRITE!

baseq2 should look like this:

[players]
[save]
kmq2config.cfg
kmq2gamex86.dll
kmquake2.pk3
kmquake2_extras.pk3
pak0.pk3
pak1.pk3
pak2.pk3
vrquake2.pk3

start: kmquake2.exe
open console
type in "map bar1" and press enter

the screen goes black and the next thing you see is the start of the first level.

You can go arround the Bar and thats it.

to end the game open console and enter "quit"

Unfortunately no animation play and you cant interact with anything.
No barkeeper or bottles are spawned.
It looks like everything that is "static" or "part of the map" will work.
Everything that is loaded extra wont work and you can see a lot errors in the console.

I think it shouldnt be that hard for some one with a bit more knowledge about quake2 mods to make it playable.