I have 75,000 Skymiles and $600 in Delta eCerts.

I would like to pay one ticket with the 75,000 miles (which covers the entire fare) for my son, and use the $600 in eCerts to pay for the second (for myself). Is it possible to do this in a single transaction?

I see that I can pay with cash, miles or cash+miles. I'd rather I pay for an entire fare with the Skymiles instead of miles + cash on each ticket.

Thanks for your help!