Yes, if you add this code to eq2ui_mainhud_impliedtarget.xml at Line 3 (right after the first <Page line) it should work for /con_version 0 and /con_version 1. I used a checkbox instead of a button since a checkbox responds on mouse down instead of mouse up.
Code:
<Checkbox Location="16,23" Name="DoAssist" OnHoverIn="ttt=Parent.v0.Name.Text
Tooltip=('Assist ')##(ttt)" OnPress="assist Parent.v0.Name.Text" PackSize="a,f" ScrollExtent="132,34" Size="132,34" Tooltip="Assist" />
I'm assuming you are using the Normal size version of the Implied Target window, not the Large size.
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