If you have any ep University or after, you can use the cheat.
Bring up the cheat console by holding down the CTRL, SHIFT, and C keys on your keyboard at the same time and type in:
boolProp allow45DegreeAngleOfRotation [true/false] True if you want it and false if you don't.
If you don't have any eps, you can try using this object.
My Bamboo Tree - 45 degree anglesHere's a link to more cheats.
Game Help:Cheats