Rout, chisel, or make multiple circular saw passes along the seam to make a dado (flat bottomed groove) say, a half inch or 3/4 wide, and no more than half the thickness of the subfloor. (I like his 1/4 inch idea.) Then glue and tack or screw in strips from the top to fit the dado. I would use strips of plywood rather than lumber so it doesn't split along the joint.
Actually, Old Engineer was suggesting that you lay a new 1/4 inch "underlayment" atop the entire existing subfloor. Masonite would work, or ply. I'd glue and screw it down. with extra care along the joints. That should stabilize the joints plenty.
2014 Sunstar 31KE
1988 Suncruiser 31 RQ
1968 Travco 210