Tips on stripping a vocal out of a track

I'm looking to make a remix of a friend's song. They're trying to release an EP soon and I wanted a remix to stick on it for them.

However, having issues trying to get an acapella of the track. They fell out with the recording studio so getting the acapella or instrumental files from them is impossible! So, no phasing possible and no straight acapella file possible!

It seems awkward cos it's been mixed strangely and the vocals don't seem to be centred, making it very difficult to lift them out.

Here's the song (it's the one called Downtown Man): Calansho Tracks