I know some people who don't change into special clothes to bike commute, but if for whatever reason that's not working for you and your pants, I'd add that changing clothes doesn't always have to be top-to-bottom thing. One of my workplaces had a fancy showering and changing area dedicated for bike commuters, with a small subscription fee to pay for cleaning (much less than the gym membership fee). However, occasional riders traveling shorter distances would often just wear their work top on the ride with bike shorts, then switch bottoms in the toilet. If you have a gentle coast-type ride into work in mild temperatures, you might be able to get away with that.
On the other hand, if a bathroom quick change doesn't meet your needs, maybe you can suggest your workplace add a changing and/or shower area to benefit all employees? That won't be an immediate fix, but nothing will change if the bosses don't know there's demand.
I like Pearl Izumi's Escape Quest bike shorts.