Sorry didn't respond to this before. Missed it. you can just setup a hotkey for this with whatever keyboard shortcut you want.
On the hotkey editor, Name the hotkey and remove the default ORDER and click on the +ACTION on the bottom left.
Select TradeQTY
Set the TradeQty field to PosAbs
Click OK to close the hotkey editor. On the hotkey list, give it whatever shortcut you want