Is it possible to continuously monitor changes in the PulledPastThreshold or Pulling state with some progress (may be Height of panel or scrolling position)? This solution trigger callback function “updateState” only once:
<PullToReload IsLoading="{isLoading}" ReloadHandler="{reloadHandler}">
<State ux:Binding="Pulling">
<!-- animate elements while pulling here -->
</State>
<State ux:Binding="PulledPastThreshold">
<Callback Handler="{updateState}"/>
</State>
</PullToReload>