I'm pretty positive that pl_waste or pl_cashworks has 5 CPs? (I think it's waste) So I'd say it's possible, unless Icarus (Oh gosh, I might not even have the mapper's name right) found some way to hack 5CPs onto the track? If 5 works, I'd suggest doing this: http://developer.valvesoftware.com/...Map#Adding_a_4th_checkpoint_.28pl_badwater.29 But making the 4 a 5.
8-9 caps it goes buggy when it hits 10 the team train watcher only goes to 4 that's why one of my maps has 8 cps on it but they not linked via a team train watcher http://www.fpsbanana.com/maps/69940 - has screenshots to see what I mean
You can work around that limit as long as you don't have more than 8 active at one time: http://www.fpsbanana.com/tuts/7383