Hi, again -
Google "Linux Seamonkey custom plugin folder" (for example) turns up this:
http://kb.mozillazine.org/Profile_folder_-_SeaMonkey
Again, I want to emphasize:
1. Java is probably NOT your problem
2. The key issue is how to override your SeaMonkey defaults
3. I honestly believe it's as easy as wrapping how you "invoke" Seamonkey into a small shell script (a script which overrides a few key environment variables), then "invoking" Seamonkey via the script (instead of directly).
The exact mechanics are something you're probably going to have to experiment with yourself (trial and error).
'Hope that helps .. PSM
PS:
Please post back what you find!