you have three choices....
1. wear cute sneakers to work (not keds, nikes, reeboks, but like prada sports, hogans, even chanel) and change into pumps for the rest of the day. i know a lot of people find this idea repugnant but i tried it out with really really funky prada sports and got nothing but compliments.
2. wear lower heels. it may only be a couple of inches difference but it saves a world of pain. there are plenty of shoes (even manolos and kitten heeled marc jacobs) that have lower heels that look as cute as high heels without the throbbing pain at the end of the day.
3. if your office locks, i would suggest (as one of my secretaries did when i worked in politics) just keeping a box of shoes underneath your desk. sort of an at-work shoe closet just like one you have at home. that way you can change into your power heels before a meeting but still sit safely behind your desk in a pair of delmans.