Nothing works in the long run but to stop overusing the parts that are getting inflamed and eventually permanently damaged.

If you can force yourself to 'mouse' with the other hand for a few months it may cut down a lot on some of the overuse. And you may want to start brainstorming about ways to get off those keys for a while. Is there somebody in the company who spends all day speaking with people, taking phone calls, very little keyboard work, who's going to be out on maternity leave or is leaving soon? Maybe you could be cross-trained to do that for several months, long enough to get your tendons calmed down. Or maybe a permanent change of duties/routines is possible. Just an idea, worked for me...