You can maybe rotate the 3 day split in a two-on/one-off/two-on pattern. In other words:
M - Chest, delts, tris
T- Back, bis
W - Off
Th - Legs
F - Chest, delts, tris
M - Back, bis
T - Legs
W- Off
Th - Chest, tris
F - Back, bis
And so on. However, hitting everything once a week would probably be better:
M - Chest, delts, tris
T - Off (or cardio)
W - Back, bis
Th - Off
F - Legs
Repeat.