Need Cheap 3-4ft LCD Floor mount for 4th LCD

[Juris]

I'm running a 3 screen Eyefinity setup with an iMac 27" in the centre backing onto a window sill. I'm trying to add a 4th monitor by mounting it onto the windows sill behind the iMac to sit just above the iMac but theres 3 problems.

1st the desk is glass so I have to mount it onto the windows sill rather than use a cheaper, and shorter, desk mount lcd pole.
2nd the only LCD floor mounts I've seen are incredibly expensive compared to cheap ceiling mounts (No idea why)
3rd I'm renting so I can't drill holes into the window sill so I'll have to weight a 3-4ft pole down somehow.

The LCD I'm looking to mount is an LG234v which only weighs 6.4 lbs (2.9 kg). Anyone know of a cheap 3-4ft lcd floor mount or alternatively is there a way to use a ceiling mount inverted & mounted onto some sort of plate attached to the windows sill.

Any ideas? Cheers.