We don't think "http://www.original.com/dataDir" is an absolute path for your data directory

Can you host elgg in an addon domain? My addon.com is actually hosted in original.com/addon (public_html/addon). The elgg data directory is at original.com/dataDir (/dataDir). But trying to specify that elicits "We don't think "http://www.original.com/dataDir" is an absolute path for your data directory." Please advise.