I just ended up solving this problem by buying the Mecatech universal steering rack boot I linked to above. They ended up having a distributor here in the US which they put me in touch with when I contacted them via their site.

That boot fits our rack if you ever need a replacement and can't find any by the way.

It has a vent port (that you can plug if you don't need it). I just ran a high temperature tube between the two vent ports and zip tied it really well to the rack. I basically created an external vent system kind of like many rack and pinions have. Seems to work fine.