Use of on camera flash to trigger slaves

I have an Olympus C-8080 8 mp advanced p&s. It has a specific setting for using the on camera flash to trigger studio lights via the slave sensors. I have had other photographers in my studio. Some have been able to fire my lights from their on camera flash, some have not (e.g. with a Canon 40D, we were unsuccessful). Or at least we have not been able to figure out how to accomplish it.

I am aware that there are other solutions e.g. wired connections via the hot shoe or wireless transmitters but would prefer not to have a wire or spend several hundred dollars on a wireless unit.

Does anyone have any experience with this problem and have any suggestions on how to accomplish this? I have tried various f-stop and shutter speed combinations and gone through the flash settings on the cameras we’ve tried. So far mine has been the only one where I have seen an actual setting for using the on camera flash to fire slaves. Any suggestions will be most helpful.