It's enticing, but most likely you'll find loose sprockets (or pairs) hard to purchase at a reasonable cost (if at all). In any case there's little benefit to be gained, because the smaller of the pair (2nd low) has to be larger than it's neighbor by a gap consistent with the 4th-3rd gap. So you'll end up spending fairly serious dough to change an 11-27 to maybe an 11-25, or at best a 11-24, which barely seems worth the effort.

Your best bet is to buy a reasonably priced non-DuraAce cassette in the range you want, and save this one for when you need it. Cassettes are wearing parts, so there's no loss setting one aside for the future, and IMO, not much sense in spending top dollar for them.