One tactic: Right after the stab, talk to the player you just stabbed.

*Pre-Stab: You want at least one person on the board that your target doesn't hate to believe that you have a chance to be stabbed by your target. The more people are talking about you possibly being stabbed, the better.

Right after the stab, chat with the target, express surprise that your moves succeeded (but don't oversell this point), your moves were meant to be a counter-stab for X,Y,Z suspicious reasons PLUS A,B,C countries were chatting about it. (The reasons are more important than the chatter) The target will look to confirm that you had any validation in suspecting with A,B,and/or C and get back to you.

At worst, your previous partner calls you a moron for not trusting him and for believing the other members. At best, he apologises. That's right, you stab him and then he says sorry. But in either case, he wants to right the ship, not burn it down.

The whole point is that he's still talking to you. He's not crying to other members that are looking to prey on his frustration, he's crying to you. Convince him that he could have helped prevent the stab and you'll soften the blow, leaving that avenue of communication open.

This works well in the earlier game and not at all late game (i.e. two way draw stab), but it's in the early game that you can't afford to blacklist yourself to a player after a stab anyway.

The worst thing you can do after a stab is stop talking to the person.
The second worst thing you can do is send: "sorry =/"