I didn't get spasms after my 6 weeks BCG, but we'll see what happens come January when I go for the first 3-week maintenance. However,I've had bladder spasm problems with just the cystos; I've tried urelle (taken 1/2 hour before the cysto) and have also tried just plain old ibuprufen, taken before and after. The thing that's helped the most is getting into a hot bath immediately after getting home from the cysto; at first, I'd do this once the spasms started, but now I've found that if I get in the tub right away, it does seem a lot better. Actually, I will say that the more cystos I've had (over two year's worth, every 3 months, to date), the better accustomed my bladder seems to get, or my "innards" are getting toughened up. Also, the urologist has found that tipping me backwards slightly during the exam seems to help with pain and discomfort, as he says my urethra is "tipped" so when he inclines me it's straight (relative to the cystoscope). I think some spasms may be due not just to the BCG itself but to the introduction of the foreign object into your urethra and bladder.
Best of luck with the rest of your BCG treatments; I'm following along behind you.