Hi
I really everything related with this wonderful tool, thanks a lot for the big effort But unfortunately it has some lacks and one of them is a nice print utility so you can print your blocks when your code starts to be something big.
This is a hand made solution I use, so take it as it is.
https://github.com/islegmar/mit-app-inventor-utils
Basically it automarizes the process of splitting the big image in small pieces and create a PDF with the single images obtained.
It is not very user friendly (scripting) but it works
I hope it is also useful for you.