So I finally got it done. Loading text seems to work like loading files. You need to create if needed a txt file and load it into the placeGun. I also selected the PLACE_TOOL to ensure a correct behaviour.
Well that works. I wish I could have the same behaviour for text that you can have when you drag and drop text from outside InDesign. When doing so, yo can place the selected text within any text container and you can have a black marker (just like when you anchor objects) to indicate where to drop the text content.
This behaviour is not exactly identical when using placeGun.
A temp afterSelectionChange combined with a conditional app.paste for the paste part?
Some simple vbs / applescriptfor the copy part?
I didn't see your answer when you posted, I actually thought from your question that you knew the method you described and were asking something a bit different.
If you are really desperate for drag and drop options the indesign extension api has different options for them that might be helpful.