use Interpolation "'" => sub {"'".$dbh->quote($_[0])};
#...
$sql = qq{
  declare \@usrid int, \@sysusrid int
  select \@sysusrid = suser_id($'{$usrname}')
  select \@usrid = $IDVALUE from $ID
  where $IDNAME = 'USR_ID'

  insert into APPUSR (APP_CD, USR_ID, USRNAME, 
   USRFNAME, USRLNAME, FNCGRP_CD, SYSUSR_ID)
  values ('A', \@usrid, $'{$usrname}', 
   $'{$first}', $'{$full_last}', $fncgrp, \@sysusrid)
};