You see, this is incredibly inconsistent and adding some massive complications. You allow the PC to do this normally, yet won't let them just say - pull out a non-magical full-blade (so the attack could never hit) to do it. What about being blinded beforehand and knocked prone in the middle of nowhere important, but not of their own choice? Would you disallow it? What's the difference?
You have pretty much no rules supporting you whatsoever, while I have the firm ruling that the Bag of Rats (and meaningful threat distinction in the RC) to support mine. At this point you're not using RAI for anything, you're purely going on an interpretation that is entirely arbitrary and basically creates almost case by case scenarios you need to specifically rule on every time they occur. I may be extremely strict with my interpretation, but it's extremely consistent and never breaks the game or any power. If you want an effect, suck it up charlie and attack something that is actually a meaningful threat. Not yourself. Not allies. A meaningful target and RAW 100% supports my interpretation.
Under your interpretation, I think a player could feel rightly aggrieved when your logic (with no rules support) can't explain why an effect works when using their +6 longsword and not their mundane dagger. Obviously in one case the attack is obviously going to miss by miles - but you've abandoned the RCs "Meaningful threat" distinction in the first place. So you're going to bury yourself in issues like this pretty quickly. Not to mention interpreting if a PC who ran, fell prone and tried to do it can't do it, while if a PC who was blinded by an enemies effect and has a -2 mark penalty (as an example), could do it.
What about effects that occur on powers that target creatures? Would you allow a PC to declare a chair as a target and then hit it to get phasing movement (I think avengers have a power that lets them phase). What about just pulling out a +2 mundane weapon and having a go at the fighter taking total defense to get the phasing movement effect?
This is just layers upon layers of nonsense that is simply stopped by what the rules already say can't be done.