Wire in a tt-30r so you meet code.
Leviton 7313 30 Amp, 125 Volt, NEMA Tt-30R, 2P, 3W, Flush Mounting Receptacle, Straight Blade, Industrial Grade, Grounding, For Recreational Vehicles, Side Wired, Steel Strap, Black - Amazon.com
Then use an adaptor that connects the hot and the neutral from...