I think going out (for walks, playing the park) etc once or twice a day would be a big help for him too! It seems like he is pretty social...and that is good....so being out and about would probably liven him right up. And there is nothing wrong with that....my two liven up when company comes here too!
To be honest...I notice no difference in Mojo since we got LilyGrace.....course, we always had the big dogs too (just not in the house while we were gone)....so, getting another dog....although that may help, it may not....soooooooo I would try more toys (interactive ones), more outings and walks, etc. AND you are at home working...what a blessing right there.....you have a lot of opportunity for all that PLAY TIME!!
I don't feel bad about asking about rehoming.....that is why you have a family here on YT!!!