How do I pad elements to produce fixed length formats?

I'm using the latest build of open-esb and Netbeans 6.1. I'm trying to produce a flat file format that is ; delimited and with fixed length fields. Using a custom encoding producing the flat file with the desired delimiter is fairly straightforward. However I'm unsuccessful in appending leading 0's in order to get the desired field length in the output file, for instance to transform 11 to 00011. I've searched for this functionality both in the custom encoder and in the bpel mapper.

I've tried searching the wiki and the forum without any luck. Does anyone know how to do this?

Best Regards
Brynjar Glesnes