CODE
websans
Arial.ttf
18
arial
medium
roman
serif
vari
websansb
Arial.ttf
18
arial
bold
roman
serif
vari
websansi
Arial.ttf
18
arial
medium
italic
serif
vari
websansib
Arial.ttf
18
arial
bold
italic
serif
vari
... only in the "Default" fontset though.
Then with the browser window focused you press B to bring up the menu, then "Setup>Font manager", and you can add "websans", "websansb" and so on.
It'll freeze for a while because it has to index every character in the font and that could probably be a little more optimized... If you're lucky, it will store all this info in the system\LinksBrowser\fonttable file the next time you go back to the home screen so you won't have to do this a second time.
Finally, make sure to check out in "Setup>Options Manager", that "Document>Font families>Variable" is set to "arial" (it should be).
I know everything could still be polished up but it's a start.