For some god forsaken reason, the working BankID java applet that my bank used (Which worked in any operating system that had java) was removed and replaced with some monstrosity that only worked in windows since it needed an external application. When a Linux version finally was released, only Ubuntu was the officially supported distro. Son of a bitch.
However I got it to work in my Gentoo installation with the following steps:
There you go. You should now be able to create new/edit/remove BankID’s in Gentoo Linux. Users of other “unsupported” distros can most likely follow these instructions with some modifications depending on their system.