Could not you train the stairs as a trick? Have you ever tried walking your puppy over an object (like an aerobics bench) and rewarding? Have you ever rewarded your puppy for standing on a phone book, or getting onto a raised dog bed?
Treat it as a trick, and I bet you'll have this issue solved in no time.
C-ATCH Pimg - DOB: 2/06, RATO, UJJ (x2), DJA, HIT, CA, CGC, High in Games, Reserve High in Standard- CPE Nationals 2014
RATCHX High Jinks vom Neuanfang - DOB 9/12 (Gotchya Day: 1/23/2013) CA, agility superstar in training