Not a new concept to SEO or marketing here, but it is not talked about that often as compared to other linking techniques.

Instead of buying sitewide links it may be better to buy an advertising pages hosted on other sites. Link to that page from many pages on that same site (which in a sense is like pointing a sitewide link on that site at that advertising page). Link popularity flows more naturally within a domain than it does across domains.

Write the pre sell page using appropriate page title, header, and subheaders. From the pre sell page deep link to various locations on your site with descriptive anchor text.

If you make the pre sell page well and the site you are advertising on is strong enough it gives you another opportunity to rank well. In fact, if your market is exceptionally competitive the authority of the site you are advertising on may allow that page to rank even if your site is not strong enough to rank.

By placing pre sell pages you do not need to worry about getting dinged for having too many (or too high of a percentage) of sitewide links with similar anchor text.

Some people also link off to other authoritative sites on their pre sell pages to help cluster their site in with other related resources.

It is common in affiliate marketing for affiliates to host pages on their sites which warm up prospective clients prior to selling supplies on another site. If done correctly pre sell pages can have a positive effect on both conversion and SEO.