Setup contract with unlimited billing

Hi All.

Patience with me please.  I'm more technical than functional, so this question might be obvious.  I couldn't find much to anything in PeopleBooks on this but our Grants group has this request.

Frequently, at the end of a project there will be expense lines that have exceeded the original amount.  This is common practice, even so that when budget checking exceeds the limit, the approval to continue with the transaction and override is not in question.  Therefore, a requirement to ‘auto-release’ these transactions is desired.  The goal is to have this functionality turned off.

(In brief words, they don't want to have to review and release excess amount limits manually.)