flyCsG

I'm not too sure how the 2 stopovers work. Does anyone know if this is valid?

YYZ-LHR (stopover 1 at LHR)
LHR-XXX (stopover 2 at XXX)
XXX-KUL (destination)
KUL-YYZ (return)

Current possible XXX's are ZRH, CDG, AMS, PRG, LIS, IST.

Thank you.

EDIT: Confirmed IST would work. Did not confirm the rest as the call agent seemed irritated from the start.