Ya gotta hand it to the engineers at General Motors. When they have a reliable and effective brake system perfected, they still keep looking for a solution where there's no problem. Guess that's how they justify their need to be there.
If you're just trying to install the adjuster mechanism between the two shoes, you just have to pull hard on one of them. An easier alternative is to put the adjuster and spring in place before installing the shoes. That way you can bring the tops closer together to relieve tension on the spring, then use the shoes as levers to pull the spring apart when you place the assembly on the backing plate.