I was told by an experienced boater that (Weather permitting) if you bring your boat to a stop gently, then drop it into reverse tick over it may well go straight. My boat was a monster until I tried this. Depending on wind and flow I can usually get my boat to go straight back. As a side issue, If I put my boat into full reverse when moving forward, prop walk will act as a stern thruster steering my stern to port. I use this to my advantage, bringing the stern in and using the centre rope.
Hope this helps.