Ability to inject javascript actions (onclick, etc.) into target HTML elements like: <input> without customForm

I have found customForm to be way too much work to invoke a very simple javascript function. I have to create and entirely new FilterPane <form> just to have this:

<input type="text" onchange="grailsFilterPane.selectDefaultOperator('filter.op.rfidTag')" id="rfidTag" propertyname="rfidTag" domain="Rfid" opname="filter.op.rfidTag" value="" name="filter.rfidTag" onclick="getRFID()">

If I inject the onclick using Firebug the FilterPane form works perfectly. But to persist this change in the code I have to create manually a whole new form using customForm to include the onclick. BTW: the customForm barfs at the controller def: filter.