FWIW - the official Apple support page for my particular issue was 'Last Modified: Nov 11, 2014' - just 15 days ago. Whatever may have been true for you & others in the past - the official word from those who create, develop, and maintain the appleID system is you -now- 'must' enter payment information in the circumstances I find myself in - brand-new mini, software update for pages 5.5.1, already had appleID but never used iTunes or Mac AppStore, and because Pages is registered to my already existing appleID, can't use another ID. I've tried it many times from many different angles, including the suggested approach you & others apparently have used ... but from my own experience & the official word from Apple is that they require the particular steps outlined in their support page.
If the workaround from the past works for some great - just hasn't worked for me, and again, given the many other questions, comments, and references on many other blogs, fora, and threads, as well as the most recent official word from Apple, seems I'm not the only one ...
Of course, if anyone can verify that the work-around still works in those circumstances - again, new Mac, Pages 5.5.1 update, existing ID used to purchase Mac & software bundle, and never used iTunes or AppStore before, I'd be glad to know, and happy to use the work-around. Til then ...
'Nuff said (full stop) 😀