You know, I've had mixed results with virtualbox in general. Some times it works and some times it doesn't and the bugs seem to be random between versions as well. Once I find a way I can understand I can get my hands on a uefi laptop for a couple of days for testing but syslinux either isn't offering much info on the subject or hasn't really gotten into it.
I saw the elilo article too and didn't really understand how I could apply it to this system. But then I'm not exactly a subject matter expert here either.
Be happy to hear if you come up with anything.