I use my script at the following link to do generally what the OP requested (in a way that fits my own data needs) – I posted this in 2013 and it has proven to be the single script that I use more than any built-in feature of DEVONthink.
I have installed this script in ~/Library/Application Support/DEVONthink Pro 2/Scripts/Toolbar, with a custom icon for the script, and then installed it in the DEVONthink toolbar. A typical case for me: as I create drafts of client work products (combined with collateral artifacts, notes, etc., for that draft) I select the draft documents and collateral and use the script to quickly make a sub-group containing that draft. My script will suggest a name for the sub-group and optionally offer to append that name to the name of the parent.