Unless things have changed, you can add the TS photos that are INCLUDED in the package (like CRT) onto your Photopass CD. We did this last year - there is a number on the print photo they give you, and you can add it manually.
We also were able to add any ride photos that we bought prints of, just not the ones we didn't pay for - which was nice because we bought one print of our whole group on Splash and then were able to add it to the CD so everyone had a copy.