I generally got a draft made out to myself and then signed the back of it and went to the post office with it. It was always accepted. Perhaps policy has changed now, I would ask in the post office beforehand.
My current account is with Ulster Bank and they have always refused to make out a draft payable to another financial institution or to State Savings. In general this is an awkward bank to deal with and I assumed that this was another example of this.
As for the question in the first post, not sure I understand the few accounts part? I presume you are talking about fixed term State Savings products such as certs. Each transaction is a one off and you get a cert for each. If you want to buy 10 tranches, you'll need 10 separate payments and possibly 10 forms. However once you are deemed to be an existing customer it may be a lot easier - for buying 4 and 10 year bonds they used to give out a card with a barcode on it which was scanned at the counter and no form was needed. I'm not sure if they issue these cards anymore or if there is another method to make life easier for existing customers.