Setting change lease to a fixed number

All,

I believe there is a way to do this but I can't seem to find it.  I want my users to be able to extend their lease but for no more than 30 days.  I don't need a request approval for it either which seems to my issue.  I don't see a way to make a policy with a hard limit.  I'm still using vCAC 6.1 as well.

Any help would be appreciated.

Thanks!