Ranked Placements Question

Sooo... I don't have a rank yet. I'm probably gonna place somewhere in silver. What I wanna know is, the fact that placement matches can't drop in LP is suddenly concerning to me. If I can gain LP through a role and that splashes into my support rank that I never EVER play,wouldn't that mean I can "boost" my own rank by just letting the LP gains build up in the support role?

My question, then, is... Is the LP loss protection indefinite on placements, or is it removed as soon as you receive your first official rank? If possible I would appreciate a rioter's input, "straight from the horse's mouth" sorta reasons.