I'm thinking of this off the top of my head here, didn't actually try it.. Back in the analog tape days, I would do the equivalent of this with 2 inch tape..
Make a mix of the section you want to slow down..Say it's a one bar measure.. Mix that down to a stereo mix.. Then treat it as a sample - load it into EXS. Adjust the EXS pitchbend to something extremely radical.... Trigger sample at say measure 49. Adjust the level of the EXS track, carefully, and then solo that track, (mute whole mix) at precisely the same time You should be able to get a completely seemless transition, between the whole Logic track, and the single EXS instrument..
You could also program a radical tempo shift, (to offset or exergerate the falling pitch of sample being pitchbended) either when mixing down the sample to be used or while playing it from the EXS, perhaps through in a programmed high, or low pass filter too..
Tell me if this works.... good luck...