easiest way is to pull in the clutch and coast back ... lighter and lighter on the brake (behind the BP) until it taps ... but if you dont have the brake down, then you're in for a new subframe.
but to answer the original question, you WONT get thrown back down .. you'll break the plastic and tail light ... they do not offer much resistance against the force you're talking about subjecting them to. the only way youd get resistance, is when you get to the subframe ... and if you're that far back, you wont be slamming back forewards
not tryng to scare you or anything ... i have a picture where im scraping seat/ subframe ... when coasting is entirely possible.
