Lump Sum Threshold

We have an ESOP where a participant can take a distribution after termination and they can sell the shares to the company.  Unfortunately, this is no longer sustainable, as we are having to repurchase shares at such a rate that it isn't feasible for budgetary reasons.

We want have been advised we should revise our distribution policy.  This makes sense -- if we can delay distributions, we can delay repurchases.

1. We want to do this for all non-terminated participants -- is that okay?  I found some guidance saying this works, and even some that says it might even work for terminated (non-payment status) participants, but that's unsettled.
2. I think the best option is to set a "lump-sum threshold," but I can't find any guidance regarding how to set that dollar amount.  Are there limits, or can we just set it at any amount we want?  I am aware that we are limited to five years of installments (unless over that ESOP threshold, but we don't have balances in excess of $1m), but are there any limits on how low we set the lump-sum threshold to be able to pay over the five years?

Is there anything else I'm missing?  Is there a better way to fix our repurchase obligation issues?