For those reading this thread, there is an online form for this. The paper form is not necessary. You can also call in. See:
http://www.nra-activate.com/
The form recognizes your current NRA membership status, and the options that appear on the page that follows depend on your membership level. For example, if you are Life or above (meaning Life, Endowment, Patron, or Benefactor), you will be presented the option to buy Life Memberships for others, or to upgrade to the next membership level ($175 for Life to Endowment, $250 for Endowment to Patron, and $250 for Patron to Benefactor). If you do not want to upgrade yourself, but still want to purchase a Life Membership for others, simply click the "I cannot accept any special offers but please activate my 2008 NRA Membership card anyway." radio button, then the "Continue Activating" button. You will be prompted for giving a Life Membership until you click on the "Continue Activating" button with a blank form. You can thus use the online form to buy as many Life Memberships for others as you want.
For those on EPL with more than $300 left to pay, a current fully-paid Life Member must call in to do this, which will also terminate your remaining EPL obligation. In other words, the paper and online forms cannot be used for such cases.
Given what I wrote above, I hope that someone on this forum can use this information to more easily sponsor other forum members.