Awesome question. Two different scenarios come to mind. Verzbickas from Illinois didn't compete for his high school and competed in mostly open/collegiate meets and national high school meets. Not a normal situation but it worked for him.
Regarding Iowa athletes: Before the season starts, unnatached, out of state etc... is ok as long as there are no ties to the school including travel and being coached by your high school coach.
Iowa academic rule: I think the IHSAA has already pre-empted this by making sure AD's don't allow unattatched athletes in sanctioned events. By doing so raises liability issues as well as the obvious attempts to by-pass the academic penalty mandated by the Association/Union to begin with. Not sure how it works with high school meets hosted by colleges but I think they operate under the guise/sanctioning of the Association/Union. Same with the Drake Relays. I wouldn't even think about traveling out of state to compete unnatached without asking first just to make sure I didn't violate other mileage/participation rules during the competitive season. When in doubt, pay the penalty for not keeping up in the classroom and get ready for your opportunity when it comes. No sense in trying to beat a system that has been well thought out.