1992 Cadillac Deville

I am not certain that you can, since all models of cadillac came standard with A/C. If it was a vehicle that A/C was an option, you have a possibility. If you can determine that a routing could be accomplished without interference, you could route a string in that configuration and take a measurement end to end. This may give you an approximate size(length) of the belt, and with a belt specification guide(usally part of a parts supplier catalog), you maybe able to find a solution through trial and error. Factoring in an idler pulley would take the work of a machinist, and most likely be expensive.