contain amounts:Date Function

I have a schedule of monthly cash flows from Jan-2011 to Dec-2050 (so 480 months). There are certain months which contain amounts and other months have $0. For the month whereby an amount is provided, I need to amoritze that amount over 60 months.

As an example, lets say in Jul-2015, I have $100,000. The new set of amortized cash flows needs to start in Jul-2015 and end Jun-2020 (i.e. 60 months). The amortized amount in each month should be: PMT(3%/12,60,-$100,000,0). How would i go about doing this? thx