have to play in 1½ hours need help ASAP: problem with light on token that is stretched

Guys I have to play as DM in about 1:15 hour .. so im hoping for a quick fix.. I have a adventure where the players enter a dark room.. when the step og a pressure plate a long line of fire appears across the room with a light of 5 ft show a small portion of the room.. my problem is because i stretch the token to reach acroos the entire room the Dynamic Lighting sees it as a larger token and so emits the light accordingly effectivly lighting up the entire room so everything can be seen.. any fix for this?

My suggestion would be a small token on one side of the room that emits 100 feet of light, dimming after 10 feet but with only an angle of 10-25 degrees... that woud give you a single shaft of light across the room occupying one row/column of the grid (5' of light)...? On second thoughts, if it is a lance of fire it would be unlikely to dim so drop that or set it to 80+ etc?