The complicated formula is how many delegates each state gets, not how they are selected.
In that greenpapers link in my previous post, some examples: Idaho get 13 bonus delegates, Illinois get 2 bonus delegates, Indiana get 17 bonus delegates, Hawaii get 0 bonus delegates, Iowa get 5 bonus delegates, etc.
There are a total of 439 bonus delegates. That is a pretty large number considering that 1237 are required to win the nomination.
‘Bonus’ delegates get no special status. They are exactly like at-large delegates.
Iowa, for example, has bound the votes of all 30 of its delegates by the presidential preference vote at the caucuses. No unpledged delegates.