Banana Republic is eager to make sure office workers know just what to wear on Casual Fridays. It's also eager to make sure those office workers wear Banana Republic apparel. So it is taking its case to the office workers'corridors of business, via its new @yourservice program. The service will set up shops on-site- with dressing rooms, tailors and clothing specialists-so workers can get clothing (as well as advice and tailoring, personal shopping and a delivery service) without having to step outside. The pilot program will be set up in the offices of HBO, Scient and Credit Suisse First Boston. The merchandise will be aimed at each company's specific dress code.