The height difference is 46m, and they are now about 2km apart (They used to be closer, but Epsom Downs station was moved about 500m north in 1989), so an average gradient of 1 in 40 would be needed. Steep, but not impossible with electric traction, but you would require substantial earthworks at the Tattenham Corner end, or a 2km tunnel.
There is also the small matter that the racecourse passes just 100m beyond the buffer stops at Tattenham Corner station!