First, yours is a very legitimate question and I'm surprised you are the only one to raise it. For those that make a living out of remoting, iMacros over Logmein or any other remoting solution would bring a lot of productivity.
However, I don't think it can work. Apparently Logmein puts up on your screen only an image of the remote page, not the actual page nor a copy of it. It then must record the location where you click and map it to the real page, thus giving the impression of remote control. In other words you are clicking all over a single image. iMacros depends on the page properties to navigate around and do its thing, but in a Logmein page those properties are not there.
I may be wrong about how exactly Logmeing works. And what you (and I) want CAN be done with a lot of work, but I don't think Logmein will do it anytime soon. It certainly would be nice if the company stated clearly its position on it instead of ignoring the issue.