You can't do them without the tickets, but you can downgrade the tickets to a one day base ticket to limit the extra cost you would have. Also, you wouldn't use the ticket so you could keep that for a trip in the future when you don't have AP's anymore.
I know the feeling though, have been doing the same math as an AP holder for a possible May trip. (something came up, so can't go, but went through the whole process of booking etc.)