I had a similar situation on my recent kitchen remodel. New range and oven. Oven was 240v 20 amp so I wired with 12/2 w/ ground, standard Romex wire. Installation instructions for oven said to tie ground & neutral wires together if no separate ground wire was available, as neutral was for any load imbalance should any circuit in the oven be actually 120v. As for the cook-top, It was wired with 6/3 w/ground with a glass surface induction burners and only required ground and 2 hots, neutral not needed, but I couldn't find 6/2 w/ground in Romex. Left the unused neutral in the panel and the junction box for the oven capped off. Possible solution for safety may be to buy a GFCI 2 pole breaker of adequate size for the dryer circuit. I know they have them in 50 amp for pools and such but not sure about the usual 30 amp dryer size.