Indeed i should make some sensible documentation abt how trigger:impulse works.
This is juts from memory as i cant confirm right now (no radiant / nexuiz on this box

)
Create a brush, texture with common/trigger
Create a small brush textured with common/origin centred at the first brush's bottom
select both these two, turn this into a trigger_impulse.
Add a target_position straight above the trigger impulse.
link impulse->position
Bring up the entity inspector, add a key of strength with a value 500 or so.
This is not a ideal , or even good, solution to lowgrav. What we did above is a weak wind tunnel rather then a low grav field. IT will also push projectiles etc upwards. But maybe it good enough for now.. maybe i should explain the last point a bit. strength 500 makes it push with 500 qu/s since grav is 800/s we get a final "gravity" of 300 (the trigger pushes straight upwards).
HOF:
<Diablo> the nex is a "game modification"
<Diablo> quake1 never had a weapon like that.
<Vordreller> there was no need for anything over 4GB untill Vista came along
<Samua>]Idea: Fix it?
<Samua>Lies, that only applies to other people.