If flag I has been displayed, and any part of a boat's hull is on the course side of the starting line or one of its extensions during the last minute before her starting signal, she shall sail across an extension so that her hull is completely on the pre-start side before she starts.

Yes, the boat can come down the extension and pass astern of the RC boat and start.

The diagram below shows another way to start correctly after violating RRS 30.1.  Assume that at position 2 is within the last minute before the start.

My comment does not answer your question ;-) please note that World Sailing very much discourages the use of the I flag because
a) it contributes to a sagging starting line (not the line itself but the boats lining up…) since
b) the penalty for a boat crossing the line early in the middle of the line is far more severe than for a boat starting early at one end of the starting line. 

While World Sailing does discourage the use of the "I" flag starting penalty, there are situations where its use is appropriate:

And in the US, college and high school procedural rules invoke the I flag starting penalty following a general recall.

Well, at least I have the answer to the question why World Sailing doesn’t throw out I and Z altogether if ‚no one‘ uses them :-)