The best way is to aquire data in advance. ID both targets and estimate their speed & course. Always shoot for the furtherst one first. The speed is likely to be the same for both. The course as well. Track the furtherst target with the PK. Try to get an accurate solution. Calculate the AoB for the second (closer) target in advance, just before you fire on the first target. Don't input into the TDC just yet. Next fire the first salvo at target #1. Quickly input the AoB and get a range reading on the second (closer) target. Input that into the TDC (be sure the PK is off else you might shoot at the previous target) and re-send the same speed as before. Now you have a solution. Should take less than 20 seconds from the time you fire on the furtherst merchant till you have a reliable solution on the closer one.
I've done this a few times and it's good as long as you can estimate the second target's AoB in advance. That's the key to the whole deal.
EDIT: Here's a rough representation:
