There's no "easy" way, because the strong name (basically, the name of the *.cache.html file initially loaded) depends on "rebind properties". While it's possible (in GWT 2.3, maybe 2.2) to use the user.agent selection code on the server-side, it might not be enough (e.g. when you also have per-locale permutations).
So, it's technically feasible, but I wouldn't call it "easy" by any mean (note however that I didn't try doing it either).