I apologize. I thought you were just attempting normal SSL Off-Load.
Here are several discussion threads of using iRules to pass Client Certificates through to the Application Server.
http://devcentral.f5.com/Forums/tabid/1082223/asg/50/showtab/groupforums/aff/5/aft/29075/afv/topic/Default.aspx
http://devcentral.f5.com/Forums/tabid/1082223/asg/50/showtab/groupforums/afv/topic/aff/5/aft/6260/Default.aspx
Guide using Firepass:
http://devcentral.f5.com/Tutorials/TechTips/tabid/63/articleType/ArticleView/articleId/141/Configuring-Client-Certificate-Passwordless-Authentication-on-FirePass.aspx