If you want glass to appear invisible, or take the reflections off of anything really, you could try cross-polarization:
1. Buy a roll of polarizing gel, you'll need to frame it, or see if you can get one pre-framed. 17x20" is a nice size.
2. Fasten the gel in front of your light source so it has complete coverage, if you use a diffusor, the gel must be on the outside of the diffusor.
3. Put a circular polarizer on the lens of your camera, take some test shots, and adjust the polarizer on the lens until all reflections are gone.
4. Ideally, the lights should be at a 35-55* angle to the glass, but this method is effective enough to almost remove the reflection of the light itself.
The only downside of this technique is that the double whammy of PL's takes off about 2.5 stops of light, but it can be fairly useful, here's a quick comparison I whipped up:
Note - the white line is a cable on the floor, not a reflection.
P.S. Oh yeah, don't use modeling lamps or have the film too close to the light, it can be damaged by heat.