1) Sign up for a Serve account using the Softcard app (Android).
2) Use Chase or Barclays CC to load $1500/mo to your Serve account without any fees. This will take 3 transactions of $500 each (limit per day), which can be set up to occur automatically each month.
3) Use Serve's free billpay to pay your mortgage, wherever that is. Collect CC rewards.
If your mortgage is over $1500/mo, it gets more complicated but is still doable through Serve.
Target's new reloadable Red card might be a better option if your mortgage is more than $1500/mo. Works mostly the same way, except the credit card loads need to happen in a store. Also helps if the new Red card is available in your area, as it isn't yet available everywhere.
Either account would also work for car payments or student loan payments.