LED Light Bar to Bull Bar

I am having trouble figuring out how to mount LED light bar to Westin Bull Bar.

I went with a 23" light bar that has the sliding brackets. My bull bar has predrilled holes. I don't believe these are threaded.

How are you supposed to mount these light bars to the bull bar when you cannot access the inside of the bull bar to put the nut on? I know some people drill a hole in the bottom of the bull bar rail so that they can fit a socket wrench through to tighten the light bar down. I would like to avoid this if possible. the only other thing I can think of is to try and glue in insert threads but I do not think this is secure for a truck/off-road.

If anyone has had a similar issue or has any suggestions I would greatly appreciate it.

attached pics are what im trying to accomplish.

 

There are mounting brackets on ebay that you can use.

 

I solved the problem. Once I actually looked under the bull bar there was already large holes pre drilled so that you can get a nut on the bottom of the bolt at the top.