I have a shower at work but sometimes I take a shower at home before I leave anyways. On those days, I take it easy and wear a tank top to maximize pit cooling and pack my stuff in my Carradice saddlebag. Anything on my back will me sweatier than usual. When I get to the office I switch to a fresh shirt. Frankly it's been kind of cold in the mornings here - at least on the bike path - even on the hottest days. Perhaps leaving earlier for work might help too.