Yep - I'm a half and halfer. Love a big thick handle
I use tape on two opposing sides of the handle, then tape round it - this makes the handle go quite oval.
If it's because of a bottom hand dominant grip - just relax up that bottom hand. Have a net - forgot hitting the ball for 4 etc - just use the top hand and then bottom hand to support the bat (no more, it doesn't need to hold on etc). A lot of the time it's due to a RH batsman being right handed - as such the right arm is dominant and therefore stronger, so often can take over if the technique isn't quite right!