I would just put some slicks on your MTB and ride whatever wheels you currently have. As you said it's never going to ride like a LHT so why bother trying? Just ditch the knobbies for long road rides and enjoy it for what it is.
My GF used this MTB with slicks on it for a year as her only road bike until we built her up a dedicated commuter rig. She has no issues at all.