@jrockisjoujou: You'll still be at the venue, even though you won't be in line the whole time, right? I think you should be fine then if you get someone to hold your spot. You'll still be there, just doing street team stuff. I don't think anyone will have a problem with that.

And the banner isn't going to be walked down the line? People might not want to get out of line to sign the banner, I think it's generally walked down the line by whoever made it. Also, people at the back of the line might not know there's a banner up front.