You can absolutely "drop transfer" or "ground transfer" items between accounts: it's 100% legal. However, it is risky: if anyone else picks up the items you dropped (while you /q and switch accounts) you will lose them. Also if the power or your Internet goes out in-between, you're similarly out of luck.
A much safer approach is to ask people in the EC tunnel to help transfer the items. If you load them up into full bags it shouldn't be that much of a hassle, and people busy selling there often have free time and are willing to help.
If you do it that way, your items are safe: if someone offers to help, then steals them, the staff will help you (whereas they won't if someone takes your ground transfers).
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