Alt+Shift+DownKey to box-select beginning of each string followed by Ctrl+V pastes only on the first line.
Alt
Shift
DownKey
Ctrl
V
1) Mark
2) Push Alt+c to open Column editor
Alt+c
Column editor
3) Enter text there
As commented by @chapo it now works fine with Alt-Shift-Down and then pasting.
Alt-Shift-Down