I have no idea if it works (didn't go into the code to deep yet), but you should give it a try anyway
PHP Code:
if ($post[customfieldname]!="") {
eval("\$post[thisisthevariableforthetemplate] = \"".gettemplate("templatename")."\";");
} else {
$post[thisisthevariableforthetemplate]="";
}
Find
if ($post[icq]!="") {
and add this above it.
customfieldname = the name of the profile field
$post[thisisthevariableforthetemplate] = the variable you put in the postbit template
$post[customfieldname] = the variable you put in the template you make for this field.