I'm not sure that they'd be useless, with 4 bulbs you're not increasing the % of UVB but the exposure to the UVB I believe. However when accounting for the 50%+ of light lost through the mesh their effect would be drastically reduced. Then there's the replacing of 4 compacts every 6 months at most - very expensive!
For a gecko where UVB is very important I wouldn't want to risk it personally.
Could you not save the canopy or use it for another gecko?