You are understanding :) But the "gist" of your original question ( how to get around Pinterest making you look "spammy" to their users )..which I gave you a suggestion that will work on..
Has now become "modified" by your latterly expressed desire to have a solution that does three things ..
1) Stops Pinterest making you look spammy..
2) Doesn't affect the search engines indexing the "new you" as opposed to the "old you"..
3) Doesn't use a method which you personally ( and which you believe others ) find "irritating"..
I can't see how you can satisfy all 3 of those ..
Unless you use the java ? ( never seen it working so don't know what you mean there ? ) that you say the spammers do..
You already know that Pinterest are not going to help you..( unless you have a couple of senators and a supreme court judge in your pocket )..yes a301 is the "recommended way"..but Pinterest are not being co-operative ..
So your choices are limited to what you don't want to do..or in the case of the "java" cannot do ..or watermark your pictures, and hope that enough of the pinners get curious..
Some problems do not have easy or perfect solutions..
You want to play on Pinterest ..it is their ball ..and everyone elses IP..
* there might be a way via .htaccess and php together..but I'm waaaay to busy to try and work out a foolproof one..( maybe some else will stop by the thread ) and the SEs would probably ding you for "cloaking" ..