Its script-able. Here's one idea, you select the items you want to paste the FX to, then move the mouse pointer over the item (take) with he FX that you want to copy, and run the attached script via keyboard shortcut (or other non-mouse input). If there is more then one FX in the source item (active take) the script asks for the slot number of the FX to copy, it then asks for the destination FX slot number, -1 is the default and will paste the FX to the end of the fx list for the selected items.
EDIT: Script is now on
ReaPack as,
Copy FX from item under mouse to selected items.
EDIT 2: The script was updated, if source has more then one FX a menu is shown so you can simply select which FX to copy.
Note: Script requires the
js_ReaScriptAPI extension which you can get from ReaPack also.