Hi Betman - where are you based? I'm in New Zealand and do exactly what you do (although I use unblock-us to get around the geo-blocking). The first thing you'll want to do is set the region of the apple TV to the United States and once you do that you'll see all the different US apps appear - can't remember whether you need to log in with a US iTunes account for this to show or not (I have my apple TV linked to my US iTunes account permanently), although from memory its simply the choice of region that matters.
Next, you will want to have a US iTunes account and have credit in it - various ways to do this:
1. Use a site that sells iTunes Gift Cards - I use
http://www.pcgamesupply.com.
2. Get someone you know in the US to buy you some iTunes Gift Cards.
3. Use a credit card that allows you to choose a USA address - for example, in New Zealand the Air New Zealand Onesmart Visa allows you to choose any USA address as do a number of the gift Visa cards.
Once your US iTunes account has credit on it go on to the appleTV and purchase your subscription to Hulu+ through it rather than signing up online - this means the charge each month comes from your iTunes account and as long as it is in credit you'll be fine.
Best of luck.