I kinda think the legitimate time travel theme would be kind of hokey and out of the tongue-in-cheek nature of the rest of the park. The original pitch with the con artists was a lot more suitable, IMO. There are ways to do it, like sdcfan88 laid out, but meh... I'd like it to have some kind of tie in with the city, as they always do. I'm sure they came up with something good.
^Have you see Maverick? Same sort of thing. Launch halfway through gives the ride more than enough juice to speed back into the breaks. Plenty of coasters with launches in the middle now actually. Helix being the most notable since it is also a Mack.