Well in an older project I helped with they went into the engine sourcecode and forwarded the full vector instead of just the Z axis for gravity allowing them to instantly change the gravity in any direction.
With blueprint only all you can really do is write your own custom character movement (starting with pawn and not use the character movement component). Get rid of all gravity and implement your own thing that just adds a force to everything in a direction.
C++ really is the way to go here.