How about ground pouring under an electromechanical relay?
Henry Ott has written extensively on this subject. There is a nice 3-4 page writeup about how to include both noisy and sensitive circuits on the same board while sharing the same ground plane using "moats" and "bridges" to contain noise on the plane without having to maintain two split planes. You can find that paper here.

His writing in that paper is specific to mixed analog and digital design, but you could apply it to this case of a relay on board with your other circuits. I've done this with some of my mixed signal (audio) boards with relays near the audio traces and this method worked really, really well.

Some clamping diodes near the relay to catch coil closure/release noise would be a good idea too if you don't have them already. You can read more about that on this thread.