I assume that you, Nan, understand the basic structure and operation of add-on instructions. If you do this should be pretty easy.
Add-on instructions use the base instruction set of the plc. There really isn't any "converting". Just copy the rungs from inside the AOI to outside the AOI. Substitute the Input and Output type tags from the AOI code with the corresponding inputs and outputs from the AOI instance you are dealing with. Add a prefix to any internal tags to make them instance specific. Voila, you are done.
If you are asking if there are any automated tools to perform this function, I highly doubt it. Those of us who have lived life before AOIs and had even seen a Siemens program have been wishing for AOIs for years. Why anyone would want to bust that apart and add all that extra code to sift through is beyond me. I suspect it is beyond anyone who would write such an automated tool as well. Sorry, you are into this the long way.
Keith