OnServerValidate: How to get a reference to ControlToValidate

I have multiple money fields that all have to go through the same validation which includes both checking that the value is a valid $ value, and checking that it is within a certain range, and finally, formatting it to the proper format.  For instance, if a field is entered as ($1000.00) we might format it to -$1,000.00 instead.  Since the exact validation occurs on all, we decided to use the same OnServerValidate method for all of these fields.  The problem is that while we can get the value to validate via e.Value, I can't seem to get a reference to the actual textbox so that we can to currentTextbox.Text = newlyFormattedData.  We have tried casting the sender to CustomValidator and getting the ControlToValidate property, then running FindControl on the resulting text, but that doesn't work because the ControlToValidate does not use the control's fully qualified Client ID.  Can anyone give advice on how to get an object reference to the ...