Im starting to think maybe the key is to chill the wort to say 60/70deg then cube it, so as to stop extra bittering from happening with big late additions? Or maybe cube hopping is better at flame out.
You can - but you dont need to. Just do a couple and see if the bitterness is a problem for you. If it isn't, then there is nothing that needs doing. If it is - then you can just tweak your bittering addition to compensate.
I find that late hops (pellets not flowers) wheher you leave them in or strain them out add extra bitterness if you no chill. The resins are dissolved in the liquid, so straining out the green matter makes little to bugger all difference, the only thing that matters is how long the cube remains hot, and how "bitter" the hops were.
In my beers - if i add a flame out hop, it works out that it give me about the same bitterness i would have gotten if i had added the hops at around the 15-20 min mark, then rapidly chilled the wort. So obviously, if the hops were 4.5% goldings thats not a lot of extra bitterness... But if they were 15% galaxy it is. All you need to do is plug your hop additions into your brewing software as per normal, then change the late additions as though they wer 15 mins earlier - then tweak your bittering addition down till the total IBU level is the same as it was before.
But thats my system - you need to work out how it works in your system. There will be an adjustment thats right for you, you just need to find out what it is. Maybe you dont need to adjust at all.
Or you can simply chill the beer instead - if you heave a full cube in the pool, its not fast no chilling, its just chilling. The beer will work out the same as if you had chilled, because you did - but you also wont be able to store it long term, exactly as if you had chilled - which you did. And all the issues with extra bitterness cease to be an issue.
Hopping is a very personal thing, even hopping is rapidly cooled systems isn't something that there are hard and fast rules for. Lots of different formulas for calculating bitterness are used, none of them come out with the same number of IBUs for the same hop additions. You just have to find a formula that works for you. If you no-chill, naturally its going to be different than the formula for someone who does chill - why on earth would it be the same? Trial and error and a few hints about where to look for places to make some changes are all you really have. Now its up to you.