What is the safest way to approach discussing a prize split?
A 'split' is only possible if everything is divisible.  It is basically just a shortcut for all remaining (generally 8 or 4) players all having to go around and individually agree with each other to evenly share any product they may win.  Then separately all going back around and all agreeing to drop from the tournament.  This is all completely allowed.  The 'Split' rules just spell out explicitly and reassure organizers (who aren't by any means expected to be rules wonks) that this particular scenario that comes up often when FNM runs late is allowed by DCI.

You can make an agreement to share prizes any way you like, then actually play the match for real and report the real result.  Or ID, or one player may choose to concede/drop.  As long as there is no link between prize agreement and match result, it's fine.

If specific match results (including dropping from the tournament) are discussed, requested or offered, it's bribery, simple as that.

Sometimes it is not possible to agree to share a prize (like byes and blue envelopes) without implicitly offering a match result because DCI requires the prize be awarded to particular finishing positions.  You are allowed to agree to split however you like only in the final round of the tournament.  Basically at this point you're not harming other people's prospects in the tournament, forcing someone to play for a prize they won't use is stupid, and forcing "fake" matches harms the integrity of the game far more than letting people work out dividing prizes they don't want/won't use.

So to your two questions:

1) Don't mention or make any arrangements about match results and you can agree to do anything you want with transferable prizes you have won or may win.

2) If you've made an agreement that requires reporting a particular match result such that one player advances to claim a particular prize, that is bribery.  If it's the final round of the tournament it's allowed for a player to drop.