Discover cash back bonus and Sharper Image?

[waharris007]

Hey guys, have any of you ever used the Sharper Image gift certificates that are available through Discover cash back redemption? I can buy an $80 certificate for $40 of Discover points. If I buy two $80 certificates, could I use them both together toward something like, oh I dunno, an iPod at Sharper Image? Some places gripe about only being able to use one Discover award at a time. Anybody tried this with SI?