Based on my experiences with power-zoom lenses on my K10, I am of the opinion that the SDM/PZ contacts should provide enough power for the in-lens stabilization system, and not just during focusing. If they can provide enough power to zoom the old heavy 100-300 power zoom lens, they should be able to move one or two small pieces of glass. remember, these contacts were originally designed for providing stable power to the power-zoom lenses, and the fact that they still power zoom on the k10 tells me that the electrical capabilities have not been altered.
From Sigma's
own website:
"For Sony and Pentax mount, the built-in OS function of this lens can be used even if the camera body is equipped with an anti-shake function"
and
"For Pentax and Sony mount, it is not possible to use AF and the stabilizer function (OS) when attaching to film SLR, Pentax ist* series and K100D DSLR cameras."
Which tells me that it does indeed get it's power through the SDM/PZ contacts.
Edit: while it says it won't work on film SLRs, if it does indeed get it's power through the SDM/PZ contacts, I wonder if it would work on the PZ series and the MZ-S?