Initially, we wanted to  have the loan under my wife's name only but my the loan officer from the builder's lending arm told us that if I am in the buyer, the RE Agent and the mortgagor (in the loan), I could use my agent commission towards closing costs and down payment.

I think a better option is to get a job in property management.

Quote from @Samuel Pavlovcik: @Nicolas Tow Your Architect is correct that it sounds like the only option for you would be to obtain a Zoning Map Amendment to change to RT3.5 or higher.

In other words, an IRR calculation.Have you ever considered doing lease options?

This way the lender is covered and only lending on the value that is legally zoned and compliant (in case the city took action against the non-conforming unit).

Quote from @Scott Trench: Why not lend? 

If that’s the case, I’d recommend considering areas outside of Dallas proper where you can still find properties with strong growth potential.Cities like Prosper, Melissa, Princeton, and Anna are excellent options to explore.

There is an incredible amount of points to consider when weighing the options on something like this and honestly, I don't recommend it to very many people at all ....even seasoned tradesmen and investors.

My agent is saying that we are unable to split the contract that way (or reduce the purchase price), so I'm trying to figure out options.

I believe it to be a little Southern California hidden treasure for cashflow, mainly class C but if you know what you are doing its a really good option to invest locally in CA with decent returns.