In Southern California, where twenty-five and thrity mile tows are pretty common, we used to do "tandem" tows when things got really busy. Its not very hard to set up, and can save valuable resourses when the jobs are getting stacked up.
I had a chance to grab a small boat this past weekend and bring two boats inside our breakwall where another towboat took the smaller one off my hands. The picture shows the two boats in tow from my single towboat.
There is a trick to doing this right. Always put the larger boat farther back, and have him steer to one side, then take the smaller boat in close, with just a little helm to the opposite side. The idea is for the smaller boat to just have some tension on his rudder to keep him outside your wake.
With this set up, make very slow, wide turns. Turns towards the side with the big boat are easier.