Mixing a track that's BPM isn't consistent? [Traktor]

[moonsnstuff]

Couldn't quite figure out where exactly this belonged but I think this is a good place. So basically if you ever use Traktor you'd know about gridmapping, it's what you do to make sure songs will correctly sync BPM and blend together. It's fantastic and almost always the simplest thing you'll ever do. But specifically I've been having some trouble with a certain few tracks. Sneaky Sound System - Big (John Dahlback Remix) and a couple of mash-up tracks. Now I see the reasoning behind the mash-up tracks not having a consistent BPM but not in a completely fresh track. I'm assuming there was some copying and pasting done in a DAW which gives me a headache.

But anyways can anyone give me some solutions to blend tracks like these into sets? Because all I can think of is either moving the grid to be appropriate for the end right after blending the beginning or shifting the BPM during the track? Any insight into this would be great.