And now you've discovered one of the downfalls of the Intel NUC platform (and other small form-factor PCs). There's not a way to do an online migration from vDS to vSS with only a single uplink. What you may want to do is move your vCSA over to a vSS on a vacant host first, then use vCenter to shutdown and migrate them to hosts with a vSS already configured. Either way, you're not doing this online, but you don't need to reset ESXi's networking settings from scratch.