I found a pretty neat workaround to this. First create a parameter (in this case [User]). Then create a calculated field:
iif([User]=0,SUM( [Profit] ),IIF(SUM( [Profit] )>[User],[User],SUM( [Profit] )))
Basically, if [User] is left at the default of 0, it will just use profit, but if [User] is any other value, then it will change all values greater than [User] value into the [User] value thus establishing your upper limit.
Sorry for the late reply, this is great!