Here's what I would do - I'd have the real value being tied to a text field that I would make invisible.
Then I would have a visible field whose value comes from the hidden field but drops the leading 1-4 if present. Something like this -
Code:
=IIF(Left(txtHidden,1)<"1" OR Left(txtHidden,1)>"4", txtHidden, Right(txtHidden,Len(txtHidden)-1))
That code seems a little clunky, but should work.
In a query, you'd replace txtHidden with the actual name of the source field, and name the resulting expression with a fieldname something like "AS myMaskedFieldName".
Looks like June7 beat me to the enter key.