I have my JB Evasion Evo mounted on FR bars. I just bought some stainless bar stock from mcmaster carr and some SS carriage bolts and made my own, similar to the factory ones but bolt spacing to fit over the FR bars. Save yourself a lot of hassle and find a metal shop with a shear/punch, and have them tack weld the bolts.
I have a similar issue now. I'm switching trucks and roof racks and the current truck has a front runner rack. I need to figure out a mounting strategy. Do you have any pics you can share on what you did?