I don't have etherboot. I use filo-0.4.1.
Doh! I guess I'm not so great afterall...
I don't really have any suggestions. The important thing I was trying to get working for you was the int21 bios calls. The VGA bios will do various callbacks to query how much video memory has been allocated, what the clock rates are, etc. My patch traps those and provides acceptable answers. After doing that I saw a performance improvement. If you could integrate those int handlers you'll get the same benefit.
Another alternative is to debug the existing problem. You can't always get everything you want without effort :^).
Really someone in the core linuxbios group needs to adopt my patch and integrate it into linuxbios, after "blessing" it and making sure everything is ok. I did all the really hard work, someone just has to make it so it is fit for mass consumption. I'll be around for answering questions.
-Dave