Infrared on regular gas grill
YES!! You can do this!! It's even Brinkmann/Charmglow who offers the solution.

Brinkmann produces a "drop-in sear burner" that bolts to the side of typical stainless steel barbecue grills.  It's called:

Charmglow Brinkmann Stainless Steel Built In / Drop-In Sear Burner 814-6805-S
This comes in a "Dual Fuel" model or a Natural Gas model.

See: https://www.amazon.com/Charmglow-Brinkmann-Stainless-Natural-814-6805-N/dp/B00FY5038K

These get upwards of 800 degrees F, plenty hot enough for searing those steaks.

I have a 10-year old 3-burner-plus-side-burner Altima/Sonoma grill that this bolts to the side of.  I'm sure it would also bolt right onto my Charmglow 4-burner + side burner unit I got at Home Depot 7 years ago, probably fit even better.

This assumes that your grill has a side table or side burner that is bolted to the side of the main grill unit, and can be lifted off and removed after loosening the mounting bolts a little.  After removing the "stock" side table from your grill, you slide this one on and snug up the bolts.  OK, all that is if you get lucky and the bolt holes line up.  In some cases, you will probably need to drill some holes through the side of your existing grill in order to mount this as a side table/burner unit replacing one of the factory ones.  Still, relatively a piece of cake.

You can get it either in dual fuel propane/natural gas model ($150 at time of writing) or in a natural gas only model (under $100 while it lasts). If you go with the propane fuel version, you may need a second tank and regulator.  Still, a small price to pay for the safety and performance of a sear burner and enclosure designed to work together.

Why cobble together a potentially unsafe "Frankenburner" retrofit of a sear/infrared burner into a grill it was not designed for, when you can do this instead?  With this sear burner and enclosure were that designed to work together, you neatly avoid the fit and safety issues that can arise when trying to mix and match replacement burners from other "real" infrared/sear burner grill models into an enclosure that was not designed for it.

On top of that, you still have all the normal functionality of the regular burners on your grill.

When this side sear burner encloser is bolted to the side of your grill, you can still use it as a side table when the burner top is closed.

See this product: 
https://www.amazon.com/Charmglow-Brinkmann-Stainless-Natural-814-6805-N/dp/B01CGX5H8I/ref=pd_sbs_86_4?_encoding=UTF8&amp;pd_rd_i=B01CGX5H8I&amp;pd_rd_r=BXAWZZS0VHB7HDE4EX3X&amp;pd_rd_w=EOx2B&amp;pd_rd_wg=Ox1hP&amp;refRID=BXAWZZS0VHB7HDE4EX3X&amp;th=1 

P.S. Sorry if I sound like a salesman, I'm just happy to have a solution that is safe, takes so much of the guesswork out, and lets me sear thick steaks without affecting/compromising any of my grill's other functionality.