Introduce him to the sisters who are your closest friends gradually...the double/triple date thing is good too. Work up to having him at a date party, don't just throw him in! Mr 33 I think at first was somewhat scared of meeting a bunch of sorority sisters, but he's gotten used to it and went to our reunion without freaking out.
The only place I'll never take him again is Homecoming, too crowded and crazy (things he detests whether they are sorority-related or not).