Well, this is real old, but I'm bored at work, so...
Prestidigitation is very low powered magic, so while you might be able to hold a rough form of yourself while concentrating on it, I would say it loses form immediately when you stop.
Arcane Mark is similarly limited in scope, and were I your DM, the short answer would be no, but the Instant Portrait spell would be fine.
As I interpret it, you are correct in that all likenesses to be sensed or possessed would need to be within the 50'/lvl range.
While I doubt that any of this is timely enough to help... here it is anyway. meh
Happy Gaming!
