What is a a P/E?
It would take a capacitor in PARALLEL with the coil to keep the relay power after the input power goes away. The resistance of the coil is R = e^2/P = 24*24/1.8 = 320Ω, so it would take C = 2/R = 7000uF capacitor to hold in the coil for ~2 sec, which is a huge capacitor. You would also have to consider how long it would take to charge that capacitor from the P/E output, whatever it is? It might be necessary to limit the current into the capacitor, too, because when the P/E switches on, that capacitor is going to look like a dead short.
Offhand, I'd say that this is impractical...