Hanging cabinets on wall with air return behind it

Hi, I've looked around, but can't seem to find an answer to my question. We're adding 2 base cabinets & 3 wall cabinets to a wall in our kitchen. When the electrician was moving the outlets up for us he pointed out that there's an air return behind one section of the wall that runs to the 2nd floor and the studs aren't 16" oc at that spot. It's 23" between the studs there. All the other studs are 16" oc. My concern is there's a 36" long cabinet going in that area, so 20" or so of the right side of the cabinet won't be attached to a stud. What' the best and strongest way to attach the cabinet here? Is there a way to do it that won't impede airflow from the upstairs or will have minimal affect on it?

Thanks is advance for the help!!!

 

Is there a cabinet on the other side of the 36" long cabinet? If so then all of your top three cabinets can be screwed together and support each other, bridging the 20" gap.

 

Correct as PD says. My son's house we ran into the same situation. Just for added piece of mind you can use a toggle bolt where there is no stud.

 

Yes there are cabinets on each side. I wasn't sure it they would be enough to support everything. I just want to be sure I get these installed right. Thanks for the help Pilot Dane and Norm201. I really appreciate it.