How big a mortgage? What interest rate? There might be some places to put the money along the way. For example you can get 50,000 miles from Fidelity for a $100k deposit. That might be a good short term move and then after meeting your co mitements to them move it to pay the mortgage. I think Schwab has some cash offers for large deposits.

And of course, can you pay it in full with a stack of money orders at a branch??