multiplying w/o formulas

Hello all!

I have run into a little bit of an issue with formulas. The idea is that I'd need to run a super-simple formula in a cell, the likes of *2

The problem is that I don't want to use a regular formula that is written in the cell, but something more in the fashion of formatting or even something else that I haven't thought of yet. The issue with a regular formula is that I'd need the result being calculated in the same cell, not in a duplicate one. The information gets there by copy-paste, overwriting the formula anyway.

I'll try to give some example - let's say a number 10 is written / pasted into cell A1. What SHOULD happen, is that the inserted number should be automatically multiplied by pre-defined number. In case the number is "2", by inserting "10" in cell A1, it should turn into "20" - in the same cell, not A2, where using a formula is obvisously super-easy.

I'm running Excel 2007 (with the possibility to upgrade to 2010 if needed). Any ideas?

Thanks in advance,
Tim