Check this out... i know a guy who uses these and likes them alot. I'm planning on trying one out myself. They're basically foam/rubber rings of varying thickness that constrict your penis similar to what the clamp does but is less conspicuous. Supposed to be very comfortable. I'll give you guys feedback once i get mine.
http://www.ctc-company.com/cart/agora.cgi?page=stallion-cc.html
http://www.ctc-company.com/cart/agora.cgi?page=stallion-cc.html