I'm pretty sure you need to re-write it. The only thing I can think of is there was a discussion a while ago about making other tools work like the orbit and pan tool, so they can be invoked while your tool is active, and not de0activate your tool. So you could try to do that with the selection tool, make it pass control to the selection tool without de-activating your script.
I really don't remember who asked the question, but it seemed like RickW, AdamB, and maybe NewOne were involved in the conversation? Hmm, I don't recall. But I am thinking maybe it would be possible.
I don't remember if "the magic" happens in the Tool.resume / Tool.suspend? or if it happens with the new .start_operation flags? Or what it was, but there was a conversation about it....sorry I can't give any better specifics. Maybe someone else knows what I'm remembering.
Chris