I hope you find what you’re looking for. Here is my take:
I’ve been learning with Ben for three years now but I skipped a lot of the basic lessons so I saw the melodics lesson for the first time just now.
It seems to me that he gives you all the tools you need to construct your own scale exercises in that lesson. As he does in G, you look for alternate notes on other strings that will help you build a smooth scale.
If you know your scales, then you will realize that except for C and G, you will not be able to use all the open strings to their advantage and that will force you to compromise. For instance, if you want to play a D scale starting on the open 4th string, then you will have to play E-F sharp single string. However, the up the neck shapes will work for whatever scale you’re in.
I might suggest though, that rather than looking for scale exercises, if you have not done this already, I would look at Ben’s melodic song lessons like his Intermediate Salt Creek or (easier) last January’s Sailor’s Hornpipe.
My biggest problem with playing the banjo is physical. It’s getting my hands to do what I want them to do. Ben’s song lessons are really less about the song and more about excercises that teach your hands what works and through force of repetition, allows you to call up these things on command.
When you can do that (I’m still working on it…) then making your own melodic exercises will be easy.
Keep practicing and have fun!