This seems to work for me.
|$find('<%= RadRotator1.ClientID %>').set_initialItemIndex(iIndex);
|$find('<%= RadRotator1.ClientID %>')._loadInitialFrame();
Found the latter function digging through the JS file. Note by calling a 'hidden' function like this you could mess up other events, etc. but for my purposes this was all I was looking for.
EDIT: oops, sorry no it doesn't...I'll keep looking...