We tried that trick too, and it got a little hard to explain when one Scout's parents looked under his bed while he was away. We also got into the habit of dropping all our tailgates at the trailhead and encouraging the Scouts to leave extra stuff in the trucks. That worked out pretty well, too.

In all honesty, the best system was to get the parents involved in the backpacking gear demos the older Scouts would show the younger Scouts. We tried to keep it simple so budgets were respected, and often loaned out gear as-needed. By involving the parents in the educational process, they became more aware of what their sons needed and how overpacking could be harmful.
That's one of the greatest things about Scouting: you treat the adults like sentient beings and you treat the Scouts like adults. Everybody wins.