readonlye checkbox in inline edit if level not admin

Dear
on tips & trick :
To hide Horsepower field use the following code in Add Page: BeforeDisplay and/or Edit Page: BeforeDisplay event.

Note: Change the values listed in red to match your specific needs.

1. Horsepower edit control will be shown only if username equals "admin".
   
   $xt->assign("Horsepower_fieldblock",$_SESSION["UserID"]=="admin");
   
2. Horsepower edit control will be shown only if current user belongs to the admin group.
   
   $xt->assign("Horsepower_fieldblock",$_SESSION["AccessLevel"]==ACCESS_LEVEL_ADMINGROUP);
   but this tips not working for inlined edit, user level still can edit the field,
   
   I need my checkbox field readonly in inline edit/add if the user level isnt admin,
   
   any help would be highly appreciate
   regards