Edit:
Simply register, print out the email they send you, get a friend to fill in the card and score 2 for 1 lunch at your nearest MYO store.
Here's the email below.
My local MYO is great, uses fresh ingredients and staff are always friendly.
Hi Charles,
Please find below your 2 for 1 offer to buy your and a friend's lunch*.
Simply print out this email, ask your friend to fill in their details on the voucher below and take it to your local MYO store. One of your lunches will be on us! Enjoy.
We look forward to seeing you soon,
MYO Team
* 2 for 1 lunch offer applies to regular sandwich, roll, wrap or salad. Valid 15 March–29 March 2009. Not valid with any other offer. By completing the above details, you and your friend agree to be contacted by MYO via email. Opt-out available on receipt of first email. One voucher per person and is to be used for a food purchase only to equal or lesser value than the item paid in full.
I guess registering with a temporary inbox/email address will get you the first email from MYO and your friend can simply fudge an address if they really dont want to subscribe to their mailing list.
(Although they do say they give you the option to 'opt out' from their mailing list on receipt of their first email)