Yes, you can and plenty of regional people do. The sim has to be certified to a certain level (D I think).
No training program is required to take an ATP checkride per the FAA. As far as Pan Am...they either want to make money off of you, or maybe they had people off the street failing ATP rides? You'll need at least a couple hours to get the hang of the left seat.
Find another sim (and an SIC)...whoever owns the sim will probably know an examiner who will give you a ride in it. I know Flight safety operates some for the regionals.
Do you really need a RJ PC type? Unless you have an overseas contract job in mind, I'm not sure how that would be worth the cost. There's absolutely no shortage of CRJ PICs in the US...