Yes but eax is overwritten by a booli, so no good for elseif.
You should be able to do select eax .. case .. end select
in these cases eax is a register.
If you are not using assembler in a function it is also possible to hijack register names, by redefining them:
function f()
sys eax,ebx,ecx
...
end function
but you won't be able to use those names in assembler inside the function. Outside, they revert to asm registers.