So we are looking at purchasing a home (new primary residence) but we will be leasing back to the current owner for 120-150 days as the current build they are working on is being finished.

I was told if I apply for a mortgage and disclose that it will not be my primary residence outside of 60 days from the point of contract that it will require a larger down payment and a higher interest rate. Is there any way to avoid this? Is it as simple as contract the new home with a move in date within 30 days, and write the lease back agreement with the current owners separately therefore leaving it still as a primary residence? 

Thanks for everyone's help.