A company called Smith Tactics manufactures an AR-15 bolt catch accessory – the Battle-Bar. It mounts on the lower receiver over the AR-15 bolt catch/release button extending it to the rear, to an area above the safety selector. The idea behind this accessory is to make bolt catch button manipulations faster and easier using the thumb of your primary/shooting hand.
Battle-Bar is made of 6061 aluminum and has a black anodized finish. It mounts on the rifle using two stainless steel anti-rotation pins, which replace the trigger and hammer pins of AR-15 rifles. It is compatible with any milspec upper and lower receivers. Some custom or proprietary AR receivers have different dimensions than the milspec, so they may not work with the Battle-Bar. Another good feature of this device is that it does not protrude past the normal dimensions of the rifle.
This is a drop-in accessory, which requires no more skills than the ability to disassemble and reassemble the AR-15 trigger mechanism. It also does not interfere and works with 3 position safety selectors.
Battle-Bar is available through Brownells at $77.99. It comes with a thread locking compound and an installation wrench. Here is a video from Brownells about this accessory:
I think this is a pretty good implementation of the idea of making bolt catch/release button reachable for the primary hand. As you know, earlier Magpul and several other companies offered their solutions to this need. Nonetheless, Battle-Bar is a different approach.