Pull-coasting is an excellent way to get closer to coasting solo. Having the support of another person pulling you as you coast makes an incredible difference and is much easier than coasting by yourself. It's also a lot of fun and makes a good pairs trick.
First, you should probably be able to pull-glide. Pull-coasting is the same ... except the coaster has both feet on the fork of the frame, not touching the pedals or tire. The puller should be riding backwards, hanging onto the hand of the coaster. If you grip each other arm-wrestling style, your arms will form a W with 90-degree angles. Keep your arms stiff to give you support.
Start by riding one-footed at a fairly fast speed, fast enough so your one-footed pedaling is smooth. Once you have good control and momentum, take your second foot off the pedal and place it on the frame with the other foot. You're coasting! Focus on keeping your body above the wheel. Your weight is farther forward while coasting as compared to gliding.
You make adjustments with your upper body. Having a partner makes this much easier! Remember to keep your arms stiff so you can depend on the other person for support. Experiment with what speed works best. Keep track of whether you fall off forward or backward, and adjust accordingly. Also try being pull-coasted in a wide circle. The puller has an easier time pulling a coaster rather than a glider because there is less friction involved.