If you want to take pictures with it, you will need to "fake" a couple of signals from the lens assembly.
So far as I can tell the lens extends and retracts during power on self test, prior to taking the first picture.
This will probably involve two limit switches, and these will almost certainly be optocouplers (A light sensitive device, probably a photo transistor or photo diode, and a light source, probably an infra red LED)
I have a couple of dead canon ebay corpses which I robbed to fix an 850IS and a SD550 and so far as I can tell this is all there is to their optical assembly, nothing too fancy from an electronic perspective. The trouble is that these signals need to be received by the microprocessor in the right time frame to convince it that the lens has extended and settled.
If you had access to a scope and a bit of spare time, you could probe the pins of a working camera, or simply switch on the dead lens one and manually operate the lens (if it is not jammed solid), or even just guess by estimating the time taken to init the lens.
This would give you the approximate required timings, which could be adjusted till the brain of the canon powers up reliably. (The usual caveat about electrocuting yourself with the flash capacitor applies,

I can tell you from experience it is extremely unpleasant, and potentially fatal, so discharge it carefully if you are planning on soldering any wires anywhere, and avoid it like the proverbial if testing with the back off).
Once you know what signals are required, you would then be in a position to convert it to use some other lens, the timing signals could probably be faked with a couple of 555 ICs or a PIC micro.
Why not remove the IR filter while you are at it, Armed with this and similar info for the lens of your choice, Frankencamera lives!
