There is a feature in Financial GPS called "save excess" and it uses a sweep account to capture excess dollars.

Most GPS scenarios that have inflation on the income generate excess lifestyle sooner or later.  The  big sweep dollars are when a fixed expense is paid off but it can happen incrementally too over time based on different things going on.

Now the bigger question is how realistic is this. You may have a few clients that at the end of the year if they have excess in their checking account they make a ROTH contribution - but that would be rare - what most do is spend the money (or maybe it's sitting on a credit card to be paid off).

You can go into step 7 and turn this feature off and the client's lifestyle will naturally creep up - its up to you.  However, you may want to keep this feature turned on to incentivize your client to keep a cap on lifestyle and try to capture these excess dollars as they will need them in the future.  That way when the mortgage or kids college pays off - the sweep keeps the lifestyle in check and auto saves the difference.