Maybe taking a cue from the much-hated (for many reasons) Patriots is not a bad one here: What about Julius Thomas or Virgil Green in the backfield as a temporary spot-player at running back? They've both been lauded for their athleticism. I realize this is a shift for both of them, but it seems with a guy who is as intelligent and loves creating mismatches as much as Peyton does, this would be a nice fit.
I'm guessing everyone here remembers all too well the way Aaron Hernandez torched the Broncos out of the backfield last year in the playoffs. Hernandez has been clocked at just slightly faster in the 40 than Green or Thomas and they are about the same body-wise (Thomas has a few inches of height on him).
The idea is along the lines of a hybrid "best athlete available" meets "next man up". It's not likely one that's suited for longterm use, but situationally, could prove very powerful. Additionally, since the Broncos are playing a team that struggles to score offensively (not saying the Chiefs = an easy win -- division foes are tough for everyone) -- but there may be a little more wiggle room here for creativity.