What is the best technique to use when splicing romex wire that will wind up in a conduit?

Wjmx,

Romex, which is a trade name of a wire manufacturer, is actual known as NM or NMB wiring, Because of the insulation material surrounding the wires, you do not put it inside conduit.

Wiring used in conduit is individual cables pulled together off small spools. In a previous posting, I suggested that it was not necessary to also pull a ground wire, however, because of a myriad of conditions that can break or impede the conduit from a true ground condition, it was apparent that ground should be pulled also.

I am not sure from your question if you were going to, but you can't splice any wire in a conduit. Splices need to be in a UL approved box that is accessible. I find wire nuts DIY friendly, and our expert here likes them.