I have twins & there were times when I was pumping (using a hands free pumping bra which was a life saver!) & would be feeding one baby on my lap while my other one was in a a bouncer sleeping next to me. Well, the baby in the bouncer of course always woke up while I was still pumping & feeding the other baby, so I would always have a bottle ready & would have to slip on a bottle holder (that looked like a stuffed animal wrapped around it) & prop it up w/a receiving blanket or towel or whatever was handy so that the baby in the bouncer would be able to be fed & I would not have to interrupt the feeding of the baby on my lap.
This next one, I needed help from someone to get the second baby on my lap, but I had a double nursing pillow that I would put around me while sitting down & then place one baby on one side, then someone would hand me my other baby & then two bottles. I could feed them at the same time this way b/c the double nursing pillow was huge & supported both babies so well I did not have to hold them while feeding & could give them their bottles, wipe their mouths & then one at a time pick them up to burp them. I liked these times best b/c I got to feed both of them at the same time & they were close to me. This stopped working however, when my son started to extremely outgrow his sister & became too big for both of them to be on the nursing pillow at the same time.
One more thing I used to do was to prop both babies upright with pillows on the bed & stuff blankets all around them so they wouldn't tip or slide & then just hold a bottle in each hand to feed them.
I definately like your son's idea/invention though. Too bad there wasn't something like that around when my twins were babies as it sounds like it would've made feeding them a lot easier!