I ran into a similar situation myself, but we had a host that was also running Enterprise at another site. Our solution, to which our VMWare account manager said "I don't see why not" was to "borrow" the license from the Enterprise one by literally swapping the license keys for a day, doing to the SVM and then swapping the licensing back.
We were in a situation where we were going to do this ONCE from DAS to SAN storage of the VM and we couldn't afford the downtime but also wasn't getting management to purchase the upgraded license for a day's worth of use.
That all said...we never got a true answer from VMWare support on whether it was legal or not. Their licensing dept. basically told us that it was "technically" ok since we swapped the licenses between the hosts vs. having both hosts running the same key, but couldn't find anything in the EULA that would tell us we did anything wrong.