Based on the text in your question, you seem to know how to Poke-Transfer so I won't give any instructions for that. (Darkgoku's answer provides that anyway) So, I think this set of instructions will help you.
1: Poke-Transfer Moltres from Heartgold to white.
2: Play the mini game and catch your Pokemon.
3: You now have a Heartgold Moltres in White.
4: Now, wait until B2 is released in Italy.
5: Beat B2 and head to the Poke-Transfer lab.
6: Poke-Transfer Moltres from white to B2.
7: Done! You have an HG Moltres in B2.