Well the other way you can do it is by scripting in your own ignoring of files of that type.

This starter of the code block well help, if its an ignored type, just do a halt or haltdef, and the dcc is totally ignored by mirc
Code:
CTCP ^*:DCC SEND *:{
  ; # correct $1- to deal with files with spaces in the filename #
  tokenize 62 $1 $+ > $+ $2 $+ > $+ $nopath($filename) $+ > $+ $gettok($1-,-3,32) $+ > $+ $gettok($1-,-2,32) $+ > $+ $gettok($1-,-1,32)
  ;
  ; # $1- now should = Dcc Send Filename LongIP Port Filesize # 
  ; # NOTE filename MAY have spaces in it but is still in $3
  ;
  ; * place what code you need here to detect an ignored file type, likely a read from the mirc.ini and a check against the legal/ilegal file types, ill leave that lot to you.