If I had him skip any PPV, I'd prefer for it to be either TLC or the Royal Rumble.
With TLC, Heyman could show up the night after Survivor Series and say that after a year of total dominance that included ending the Undertaker's streak, winning the WWE Championship and steamrolling through people in four straight successful title defenses (he didn't lose the title at NOC, so his DQ loss shouldn't count), Brock Lesnar is gonna take the rest of the year off and has The Authority's permission to do so. (Although I'd love to see Brock in a TLC match.)
With the Royal Rumble, the Rumble match is the main attraction of the PPV, so you could either have Lesnar show up after the match and confront the Rumble winner as a way to build up anticipation for the main event of Wrestlemania, or you could just have Heyman show up at the Rumble PPV and conduct an interview backstage right before the Rumble match (or give an in-ring promo on Raw six days before the PPV) where he says Brock Lesnar is/will be at home watching the Rumble match to see just who will have the stones to challenge him for his title at Wrestlemania.