Use ISO_Level3_Shift as Escape when tapped

I use an alternative keyboard layout that uses CapsLock and # as *ISO_Level3_Shift* modifiers.

setxkbmap de koy

I also like using CapsLock as additional Escape key when it's just tapped. This can be easily reached by:

xcape -e "ISO_Level3_Shift=Escape"

But this makes both Level3 modifiers act as Escape. How can I apply xcape only to the left modifier key (labeled CapsLock)?