No, there isn’t a way to do this unless you have a router which supports Quality of Service. You wouldn’t want to carve a T1 up to support 20 users unless all 20 users are using the T1 at the same time. A T1 is 1.5 Mbit / sec. Cut up into 20 parts that is about 76.8kbit / sec, or just faster than dial up.
Let the users get all the bandwidth which they can get when they can get when they need it.