I think Hulk should be willing to sign quite easily. Dzeko I'm not so sure - in my games Man U usually snatches him up in the first season which pretty much puts him out of bounds.
Scout them, see if they want to sign, see if you can afford it.
If not, you can always try offering 2/3 of your total budget and the rest over 48 month or after x goals, apps, etc, with percentage of profit from next sale etc.
You need to able to cover at least a few month of the monthly installments from your current budget for it to work (e.g. you can't offer 10 million and 12 million over 48 month if you only have 10 million to begin with - where would that money come from...?)
Anyway, when I saw Man U get Dzeko last time, his value was at 10.5 million, so I guess it's within your budget. And he might very well prefer Premier league over Wolfsburg. And just offer them 50% of next sale or even more, I doubt you'd ever want to sell him anyway....