I agree, the three-paycheck months are great for building a buffer, and if you can also chip away at your previous paycheck by budgeting well you can be buffered even faster
For the mortgage: another thing that many people recommend is taking your 26 payments, totalling them up, and then dividing that by 12 to find out what your "monthly" mortgage payment would be. If you save THAT amount every month, when your next 3-payment month comes around you should have enough in the category to pay it without having to budget an additional payment. In numbers, it looks like this:
26 payments (every 2 weeks) of $150 = $3900 (average of $300/month, with 2 months having an extra $300 payment)
12 monthly payments = $3900/12 = $325/month or an extra $12.50 each pay period set aside
Obviously no one has a $300/month mortgage payment, but the numbers work well. Even if the mortgage payment is $500 every two weeks, you only have to set aside another $85 or so every two weeks to save up that extra payment every six months.