I'd be leary about installing the toilet without using the screws at the back (I'm assuming you are talking about a unifit adapter?). You could maybe rent an IR camera, and find where the tubes run...assuming the heat was on, they'd jump right out in the picture.
I know when I installed mine...I opted to not run the heating tubes behind the toilet so I'd have no chance of hitting one when installing the Unifit adapters.
If you still have a film camera, you may have to look hard, but you can buy IR film. You'll need a dense red filter on the front, too. It isn't immediate (since you have to get the film developed!), but this should work as well.
A really good bead of silicon, though might just hold it in place well. Hassle is, if it doesn't, then you might break the unifit, since it would torque around the flange connections - you've got a decent lever there.