It's Still a Band-Aid
Whatever you do to improve these desktop web forms for mobile users, don't let it be your end game. The facts remain: We spend more hours staring at mobile screens than desktop screens, and it's estimated that mobile web usage will surpass desktop usage by 2015. The message is clear: Sites that work poorly on mobile devices are soon going to go the way of the 8-track tape. While curious and interesting, no one's going to run out and actually use one. There are better options, and no one has the time to waste on a company that can't even bother to adapt to its customers’ needs.
Everything I've recommended here is a short-term solution. Do these things only long enough to sic someone on the real problem. Improved desktop web forms are still desktop web forms. They're not meant for mobile, and they're not optimal, and they'll get in the way of your progress as an organization.
Find them and replace them.
But if you must wait to do this, consider making these small tweaks in the meantime. Anything you do to make your users’ lives a bit easier will be appreciated, even if that appreciation comes is no better than slightly decreased annoyance.