How can I make a Bum Rush easier?
Yes! You can blitz easily with Sabin by only pressing the cardinal directions - you don't need to make a full circle or push the diagonals, just tap the directions in order, and he will do the blitz just as well.
The Final Fantasy Wikia says that you must tap Left, Left, Up, Up, Right, Right, Down, Down, Left.
Also note that it doesn't matter which way Sabin is facing (ie, if you are in a back attack or pincer attack, where he might be on the left rather than the right) - the directions are always the same.