Actually I don't think this will work since the edit in list box that pops up when you click the button references in the form code
<pdm_jscript file=list_edit.js>
Which you would have to add a ListEditRequired function.
The List_cr.htmpl has this in it:
<pdm_jscript file=list_edit.js>
startListEdit(__search_filter);
listEditStartRow();
listEditReadonly("ref_num","Request #");
listEditField("status");
listEditField("priority");
listEditField("parent.ref_num");
listEditField("caused_by_chg.chg_ref_num");
listEditField("assignee");
listEditEndRow();
listEditReadonly("summary",4);
endListEdit()
I don't believe CA would support modifing the list_edit.js file