jacking up the three 4x4s, putting the pipes underneath, does seem the simplest route.
So are we talking simple 2" diameter iron pipes? just over 12' long?
I'm picturing the pipes getting jammed down into the frozen ground as we roll the shop forward. Not good.
Edit: also worrying that if those 4x4s are somewhat buried in the gravel/earth, there'd be a major problem getting jacks under them for the entire 12' length. Jacking up the end and putting pipe under the end would be tough enough; but rolling the 4x4s forward, if stuck in the earth, would seem next to impossible. That's why I wondered if raising the workshop so the pipes could go *on top of the 4x4s" might be more do-able.