I have a Pearl Izumi convertible vest/jacket, and I've often wondered if I could just take the vest part off and wear the sleeves part, instead of the other way around, since usually my core gets hot but my arms are still cool if it's chilly out. Isn't this essentially what the bolero would do?

It's not snug-fitting so perhaps it would flap around, but I wear a camelbak while riding so I suppose that might help keep it in place? I looked at boleros online and it looks like many of them don't have any zippers or anything to keep them closed/snug in front - how does that work for people concerned with aerodynamics/speed?

OP, if this would work, perhaps this type of jacket could serve dual-purposes for you?