Your dryer is what it is, the fundamental design of it can't be changed. The uber-sized models that are common nowadays may not handle a load of just one or two pieces very well. The tumble speed and drum baffles have to be designed for handling a full-size load. The only reasonable workaround is adding more items, such as the towels you mention, to make for a larger load that will tumble properly.

A bit of trivia: Whirlpool offered a couple top-of-the-line dryers in the early 1970s with three tumble speeds. A slower speed allowed better tumbling of lightweight items such as lingerie, and a faster speed for heavy/bulky items.

I know someone who put a tennis ball in a sock and pinned the sock to the shirt so it would tumble. Sounds wacky but I guess it worked. You might need to adjust the weight depending on the shirt. Those plastic dryer balls may work, too.