I just have to thank scp1127 for the FABULOUS suggestion. I didn't even post the original inquiry, but needed to make banana frosting as well.
I made Brennan's Bananas Foster (first time flambe-ing...so much fun), let it cool down a bit, put it in a food processor to puree it and added it to a fresh batch of SMBC.
Oh. My. Bananas! The frosting has an AMAZING depth of flavor that you definitely wouldn't get with just mashing bananas.
Thank you thank you thank you...and add like eleventy-four more thank yous!