Slow shutter speeds for IR photography with the A620

I posted s little while ago about being exited to learn that my old PowerShot A620 is well suiting to IR photography, something that I've been interested in doing since my experiments doing that sort of thing with Film 20+ years ago. Anyway, I'm still not there yet having received a filter that I ordered but not yet the adapter to mount the thing to the camera. I realize that a lot of questions will be answered once I get everything in place and do some experimentation, but for the time being I thought I'd ask you folks about what I see as a potential issue... The filter I just received is a very dark, 720mn value, which is my preferred starting point for this IR stuff. I figure if I'm going this route at all, I'm going to want to really emphasize the effect and this filter seems like the one to do the trick. I'm realizing that with this filter I might have to do some very long exposures and in checking the camera out just now I see that the lowest this thing will do is 15 seconds. Is that likely to be long enough with this particular filter? If not, is there some sort of hack for getting a longer exposure out of it (maybe a way to get to a bulb setting that I hadn't seen)? If that isn't possible, I guess that I could use this 25 filter that I just ordered (25R I think?) instead, but that option is less attractive to me because the IR effect with that is surely going to be much more subtle (not really the effect that I'm looking for). 
It'd be a shame if after ordering all of this stuff and getting really exited about using my old A620 for this brand new thing (and in the process "recycling" it), I'm not going to be able to do what I want to do with it. In that case, I wonder if there's some other old point and shoot that like my Canon has weak IR filtration, but also has the option of slower shutter speeds (preferably a bulb setting) and/or more sensitivity (higher usable IS0)... and of course will have a sitting for an adaptor to hold a filter(preferably 53mm)? I figure that these old point and shoot cameras go for so cheap that I might be able to find the right one for next to nothing on my local Craigslist if I spent some time shopping for it.