Combine the Groupon here : $50 for $100 in online Credit at Charles Tyrwhitt
(See right hand banner under New York, New York for deal)
The following promo: 1 Shirt + 1 Tie for $40
and in total you get.....
2 shirts + 2 ties + $20 in additional credit for $50
Note: Although the 1st offer states 1 shirt 1 tie per order, you can indeed order twice, either through a different address, different name, or wait until the initial order ships. If you plan on doing this, use guest acounts
ALSO: if you want to get cashback on groupon (%3 with this site) http://www.mrrebates.com?refid=526716