Creating Proxies from Footage w Baked in merged Audio?

I'm editing some footage that was shot in 4.6K on the Alexa 35 and they ran audio staight into camera, which means the .mxf files have baked in audio embeded into the raw files -- so the footage comes into premiere like a merged clip, which means I am unable to turn these very large and sluggish files into proxies. Unless...is there a workaround?