Here is a general representation of the one I use. You take a piece of some spare panel board, osb, mdf, particle board, or ply and attach four strips to it. The strips can be 2x4 or whatever you have as long as they are thicker than your cutting board. In the center will be your cutting board and four spacers the same thickness as your boards. The width of the spacers depends on how far in you want your drip groove to be. If the distance from the center of the router to the edge of the baseplate is 3 inches and you want a 1/2" wide groove 1/2" in from the edge you would want the spacers to be 2 1/4" wide for example.
The cutting board has to be tight in the frame or you will get a wobbly line. You can shim them tight or slot two of the guide rails. In the photo I show two boards with black marks that indicate slots. For multiple boards this would be the best way to go. Snug those two guide rails against your cutting board. The black mark on the end board is there if your cutting boards have a handle. Cut that section out and slide them under.
I purposely left a lot of space between the corners to make a point. Unless that distance is greater that the distance from the center of the bit to the edge of the baseplate it won't make a difference. When you rout the groove you go in a clockwise direction. Unless you are going to make a lot more cutting boards then take this one apart when you are done and save the good parts and burn the rest. It only takes a few minutes to build this jig and it cost virtually no money so why have it take up valuable shop space? Jigs are to get a job done, they are not THE job so it doesn't make sense to spend money on nice wood and brass fittings when you don't need to. Save that money for buying bits and hardware. You can't build those.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.