Page Numbering on one side only, aligning the numbers to the left: 14 | 15

I've been working on a 220 pages art book. I want the page numbers to appear only on the left-hand page in this format: 14 | 15. The even numbers were positioned normally on the left master page. The odd numbers, however, were positioned on the right master page and then moved to the left page, as I learned from the discussion How to add Page Numbering on one side only I also added a vertical line between both numbers. It works, but I had to align the even numbers to the right and the odd numbers to the left, and this way, the numbers grow from the vertical line to outwards. The problem is that I want the numbers to be aligned to the left so that the left margin remains always the same, 25 mm. Is it possible? How to do it? You see, at the beginning of the book, the caption aligns with the numbers. But at the end of the book, when the page numbers are higher than a hundred, they don't. Thanks!