Most remote controls provide ample momentary closures for a command, but there are times when a maintained closure is needed.

This circuit requires a momentary closure for the on command and momentary open for the off command. I first saw this used as a door alert at a college radio station. The maintained closure would light an indicator until it was reset.

Keep in mind that when all power is removed, the relay will de-energize and reset the command. If the momentary-to-maintained control is of a critical nature, a magnetic latching relay or something similar is a better choice.