The exact procedure depends on the firmware. The easiest thing is to set up master accounts (thogh not available for basic users) You can configure the router to wither allow a certain mac address to bypass the splash page, or if you are using DDwrt you can create a second SSID that you can connect through. There is an article in our knowledge-base which helps guide you through:

http://hotspotsystem.com/deskpro/kb_article.php?ref=6485-RADL-1060