custom input mask that automatically fills in spaces with zeros

I would like to have an input mask that fills in spaces automatically with
zeros.

So, given a user typing in the numbers 0 7 1 2 , on lost focus the value in
the control would look like GO-07-0000012. I thought I read somewhere that
you can use an asterisk before the character you'd like to use to fill in
spaces, so that if I put *0 somewhere in the expression, it would know to
replace blanks (the blanks after the secon dash in this cases) with zeros. I
dunno.
Thanks!