How do you do it? Just run a cord from each output jack, one to each cabinet.
Is this a safe combination? There's some debate on that. While the Concert Lead is rated to 2 ohms, at least one knowledgable person on this site has said that, in his opinion, the Concert series amps do not have enough output devices to run safely and continuously at 2 ohms. I don't think the incerase in power between 4 ohms and 2 ohms makes a significant difference, and wouldn't do it. I'd prefer two 8 ohm cabinets. But, in your case, you already have the two 4 ohm cabinets. Bottom line: your amp, your call.