This has already been implemented in beta v3.1 so, if you totally need this feature you can write to the support department and ask to become a beta tester. I did not have any problems with v3.1 so far: it seems totally stable except from some minor imperfections. Nothing critical so far though.
We already have quite a few requests for this feature. Will implement it in the next release (3.1). But unfortunately not within the next week.
(I was the one that initially decided that variables in mouse location properties where not needed. Guilty as charged...)