Car seat fits adults- a trial on Britax "original" frontier

I have an original Britax Frontier however I can't fit in it properly, my shoulders are too wide. I took out the harness and use it with a regular "gaming chair" and it's just fine. I do wish there was a cheaper alternative to something that would fit me out of the factory... if only they sold this: http://infasecure.com.au/blog/wiggly-car-seat-check/ :sweatdrop: