Both Bruce and Jim gave you great answers. The "buy-down" approach Jim was mentioning is actually a great way to help your buyers get qualified if it's a question of affordability. I've seen the "3-2-1" buy down program work great for that kind of situation.
Also, like Bruce spoke about "taking a second" may be a one-two combo that may just make it work.
As I agree with Jim, there's a lot of pluses her to make this work w/ your tenant and alot of costs that it may help you avoid; so working with them as much as possible is a good idea.
an example of the way a seller paid interest rate buy down works: Seller pays buyers lender at close of escrow an amount equal to 4.25% of the loan amount. - In return the lender lowers the interest rate for the buyer by 1% for the first five years of the mortgage. - Take note that this strategy saves the buyer more in interest costs over the five year period than it cost the seller upfront.