Hi Samuel,
This is really going to depend on the type of customers the Fortune 500 company is targeting so I will go with your JCPenney example.
1. Partnerships - Find out who heads up business development and review the sites of every partner. If the partner does not have a link to you then get the Biz Dev person to call them up and ask. Another good tactic is to send a gift basket outside of the holidays, then follow up with a call asking. When a partner page already exists on the site it is easy but if you are major partners then you can ask for one to be built.
2. Charity - Does the company or employees participate in any charitable work? Check out the charities for donor pages and get your site listed if not already. Partner with the charity to do a local or national fund raising drive, hit up bloggers who are fans of either the charity or brand.
4. Identify Brand Advocates - Find the mommy bloggers and others online (forums included) that talk about your brand, competitor brands, the products you offer, etc and engage them. Let them hold a contest on thier blog for a gift certificate is a simple example. Coca Cola
5. Sponsored Blog Posts - This falls a little bit on the more risky side but it is an option. Vacations to Go has employed this so take a look at thier backlink profile for further insight.
6. Offline Marketing - Bridge the gap of offline marketing by creating a page or minisite for each offline campaign that points back to the main site.
7. Coupon / Deal websites - There are hundreds if not thousands of sites that feature coupons & deals by major companies. Dig in and find them. A good tactic is searching twitter, google, technorati, etc for words such as coupon, deal, rebate, sale, discount, promo code, promotion, promotional code. Create a list of the sites and submit your coupons & do an outreach campaign to the bloggers / twitter users.
8. Conferences - There are both industry & consumer focused conferences. Become a sponsor or speaker and get listed on the conference website.
9. Create a Youtube Channel - Make videos about interior design, cooking, back to school shopping, etc. However people use your products make videos of that, just be helpful. There is a reason Oprah, Dr. Oz, Food Network are so popular.
I could go on but this should give you a good starting point & keep you busy. The idea is you need to energize & engage the people who already use your products and leverage that to expand the customer base.