As in Sabres trade player X and keep half the cap hit and then later with a different trade of player y the other team takes player x's retained cap hit? Haven't seen that. Would be too close to paying cash IMO.
I also think that if player x gets traded and the new team trades him again, his contract could be split up again with the third team. But the first team would still be on the hook for the first trade cap hit/salary. Kinda like re-entry waivers.