You don't need to communicate it to users. If they ask, and you can truthfully reply:

> We are contractually forbidden from doing this, and if we do, you're entitled to [insert compensation plan that would cripple the company, without a private equity-style (or other) takeover being able to game it for profit] – on top of any legal obligations.

then they'll probably sing your praises… if they believe you. So maybe publish a blog post or something about how you bullet-proofed the commitment (with lots of details)? Added bonus: I'd learn how you managed it, because it's too hard a legal problem for my amateur mind to solve.