That's a great question. To do well in GP local, you're going to need the listing, citations and clear NAP on the website in Schema format plus a KML file and geositemap uploaded to WMT (Webmaster Tools). You should also geo-tag the site. All of that stuff makes the site really relevant locally, so it just may make it less relevant nationally. I guess it depends on the keywords, too.
If you think there's enough business to be found locally that it's worth it you could try this:
1) Create a landing page that's optimized for the local-ness of the business. See here to get some hints as to what should be on that landing page: http://www.davidmihm.com/local-search-ranking-factors.shtml
I would make that page at a URL like http://www.sitedomain.com/city-state/ (ie: /new-york-ny/)
Geo-tag that page, put the citation in schema format, create a KML file and link directly to it on that page, place a couple of reviews in schema format on that page, etc. Of course, I could write a book on all the other things that should be done for local, but that should give you a good start.
2. Leave the local-ness off the rest of the site.
3. When creating links with geo modifiers, send them to the landing page
4. Send non-geo links to other pages, etc. as you normally would.
*** This is ALL theory above LOL I do Local SEO only, so splitting them up like you've asked is uncharted territory for me.