Mmm, 'just realised the BCM5751 kext is 32bit only, so if you're still booting with option x86_64, you won't have Ethernet, true.
I take it you've been unable to install Chameleon Wizard and update to Chameleon v2248 or above, right? Try and boot off your myHack USB installer, then interrupt Chameleon and select your Lion HDD partition to boot Lion. If that fails, I'll send you the Chameleon boot file to copy to the HDD root.