how to use Edit Mask in Fieldcat

hello all,

how do we use Edit Mask in Fieldcat,

like i want to change WBS from S000101010101002 to  S-0001-01-01-01-01-002

for this how do i use Edit Mask in Fieldcat....(instead of using explicit conversion routine)...

  clear wa_fcat.
   wa_fcat-col_pos = 16.
   wa_fcat-fieldname = 'POSID'.
   wa_fcat-tabname = 'IT_MSEG1'.
   wa_fcat-seltext_m = 'WBS Number'.
   wa_fcat-outputlen = 25.
   APPEND wa_fcat to it_fcat.
   clear wa_fcat.

thanks in advance.....