Specifying space-before relative to the page margins

I have on a book title page several elements (title, subtitle,
    author, contributor, mediaobject etc) all centred below each other.
    For each element, I have set space-before values which are, of
    course, measured from the preceding element (so, the space-before
    for subtitle is applied relative to the position of the title).

    Instead of specifying space-before for each element relative to the
    preceding element, is it possible to specify the space-before
    relative to the top margin of the page?

    
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      Dave Gardiner