Kemulator and sjboy are both Windows only and I can find no source so no chance of porting. I can't even find an official website of any kind for either of them. The only way to download them seems to be through mediafire or other third party bulk download sites.
There's a third one, MPowerPlayer, which appears to be pure java, so in theory it should work, but I can't get it to work in OpenJDK. It seems to work fine in the official Sun Java, but the official Sun Java can't run on the Pandora, only the open source release. I don't think MPowerPlayer is very good, anyway: it looks more like it is trying to sell its own games than let you play what you have.
If you can find another option, we may be able to get it to work, but the top three programs I found will not, unfortunately.