What bike you referring to? I put one on my 1100 but had to make a bracket for the top of the bar to mount to the frame.
I don't believe any bars are designed specifically to mount with board extensions.
2006 V-Star 1100 Classic
Silverado windshield and passing lamps
OE Highway bar with custom mounting brackets
Kuryakyn Dually ISO Highways pegs
Barons Nasty Boy Slip-ons
Kuryakyn led headlight halo