no sweat ... if possible

I am doing a remodel of a 1950's bathroom. I would like to put shutoffs on the sink faucet inlets. Current fitting is a sweated elbow (see pic). I would prefer to avoid sweating the connection so I tried a 3/8 compression valve (pic) but it leaks. I did try to torque is a bit with a wrench but still get a drip. The compression lines do not leak because they have a rubber seal face whereas the fitting does not. What options do I have to avoid sweating on a new elbow? O-ring in the compression fitting, adapter ...? Thanks.