Yes, you can also put into your normal skillbar just per Drag and Drop, except you disabled changes to your skillbars in the options or with a shortcut (my own shortcut is "<", but I don't know if that it the default one; at least on German keyboards that key is located in the bottom left row). Wenn you disable changes to your skillbars you can't move any of the skills on it, can't add any skill/item to it, and can't delete any skill/item from the list, so it's pretty easy to get to know if it's enabled or not. If changes aren't disabled, drag and drop will be enough. :)
Other hints than that: I have my mouse pretty much over this popup skillbar all the time, while using F10 for choosing the chicken, wasd for moving, and the hold right mouse for turning (when the right mouse is hold, a and d move you sideward instead of turning), so I don't have to move my mouse away from the bar except for selecting other players for the rotten egg. ;)
In one game I was playing with on eother player against 3 and we one, after getting behind 0:1, then tied, then they got in front again, and then we won with 2 players against 3 with 4 goals... It was fun and really exciting and a challenge, but until shortly before the end it wasn't that clear, that we will win, so it was lots of fun.