Sorry to keep commenting on an old post but some solutions I have been considering--

- the larger one-way air deflectors that fit on larger vents, but serve this exact purpose, might be an option: https://www.amazon.com/Elima-Draft-Commercial-1-Way-Deflector-Diffusers/dp/B01BWZ90HK

- there are other commercial "linear" air diverters that could be indicated potentially

- you could get a pack that overlap and cut a hole in one side: https://www.amazon.com/dp/B0994NQ3MM/ref=sspa_dk_detail_2?psc=1&pd_rd_i=B0994NQ3MM&pd_rd_w=g2BkG&pf_rd_p=0c758152-61cd-452f-97a6-17f070f654b8&pd_rd_wg=IKvvO&pf_rd_r=1S1QGF99H4BSFPRWN0NE&pd_rd_r=274d6c18-e82d-42c4-a40a-883c3f4a5705&s=hi&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEySzVKWFBUQlJXRkJWJmVuY3J5cHRlZElkPUEwMjMzNDM5MjFKWko0VlNWSFM5NSZlbmNyeXB0ZWRBZElkPUEwOTcyNTY4M0pJQVdWUDJRUkdTNiZ3aWRnZXROYW1lPXNwX2RldGFpbCZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=

for folks with floor vents:

- you could just use the under the bed diverters even though they are unnecessarily large and jsut orient them the other way, affixing them to the carpet

https://www.amazon.com/Ventilaider-Magnetic-Extender-Furniture-Registers/dp/B086TWZ97Y/ref=asc\_df\_B086TWZ97Y/?tag=hyprod-20&linkCode=df0&hvadid=459724827079&hvpos=&hvnetw=g&hvrand=439829891820071280&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9051713&hvtargid=pla-944188383528&psc=1

If the extender is under 2" high (I was thinking something like this), wouldn't a 2" clearance be fine?

Did you have something better in mind that you could recommend as an extension for the vent?