Yance,
Wasn't able to see why the data is inserted without the leading zeroes, as the DB table looks ok using SE16n.
Nevertheless, as further evaluation of the table contents shows that this is a sparsely populated field, it was decided to use a LOOP AT construct which, along with the proper concatenation of zeroes helped us to solve, albeit a little bit inelegantly, our problem.
Thanks for your help,
Luis