Chris,
Thanks for the suggestion.
I could, in principle, create a storage profile containing only this datastore, but there are two difficulties I can think of:
1) Assuming the datastore is in a cluster, I am not sure I can create a profile that contains only a single datastore out of a storage cluster.
2) Once the import is done, if I try to change the storage profile to the real storage profile that I want to use, will this not result in a clone?