At this moment you can only chose Projects in the ABL Scratchpad runtime.

Buf if you have a project with multpiple runtime environments(development, production, ...) it's not possible to use them from the scratchpad. It should be a good idea if there is also a possibilty to add run configuration of the type "Progress Openedge Application" then you can chose your own database set, propath, project etc...
On this moment you can chose in the common tab "Debug" and "Run" the option "ABL Scratchpad" would look fabulous over here!

Ps: Yes you can create a .p file in your project and use this but it's not the same.