We can buy inserts for typical Wilmad NMR tubes. I'd recommend the 507-pp linked below. The corresponding insert tube is linked below as well. The insert tube can be filled with your locking substance such as CDCl3 or whatever. It will be 60uL total at the stem. The main tube can be filled with your fully protonated system at 500uL volume. Now it is separated from the deuterium and you'll still be able to lock and shim. The inner insert could also be used as a control compound for VT, a free ion such as in binding studies, or for small volume samples (60uL).