There also rail add ons that mount to your existing hand-guard.
I linked the first one I found, no recommendation, just an example.
It is wedge shape to accommodate standard fore grip.
I added one. I decided to neatly drill and tap my rail for a cleaner mount, but they come with the necessary hardware.
I added one on top for a 45 degree light mount. didn't want sharp edges around the rest of the fore grip.
Remove grip, bolt in place, Re-install grip.