The dual tax bill idea and 2 chains may be the answer. 

In a nutshell, sounds to me like it's a similar type of ductwork issue that I faced and most likely you'll either need to upgrade the ductwork throughout the whole house, put in a separate system coming from the attic to the top level (dual zone is quite expensive though), or you could just provide your tenants with some window units (which is what I did in one house and they were ok with that). 

Good brand non contact voltage as mentioned earlier.

Single hose models are really inefficient, because they constantly blow conditioned air outside, but the dual hose models work pretty well.

I like some of Beth's theme of things that do double duty (like new door mats and bath mats, which are dual purpose gifts that also protect your property from grit and moisture!).

I really wanted to help them.The things started bad pretty much from the beginning.Ten days after they moved in, someone broke their window and I had to replace it: about $300 - parts and labor - dual pane window replacements are not cheap.

Curious, I look up the house they were evicted from, it's a 3800 square foot 5 bedroom, 4 bath house, with 3 car garage, full finished basement, dual stair cases.

I suspect they took a tenant that paid up because they were having trouble getting accepted as tenants...a nice dual income family being what most landlords prefer.

What will change is that the listing agent will be dual agent, representing you and the seller.

Home warranty + reliable network of technicians / handymen dual strategy: I am utterly underwhelmed by the speed and quality of the services provided by home warranty.