Somethig occured to me a couple of nights ago.
There's no easy way to rez an object when you're not on your home turf or on friendly ground.
Why is that? That doesn't seem particularly fair, and makes using transport like cars and planes very difficult.
What about this: Add an item in the Inventory Context Menu called "Use". This would be analagous to the "sit" pie menu, which is typically used as the entry method for most scripted items. Clickimg this would rez the item, place the avatar in the sitting position, and allow other avs to ride along. Bjt an internal flag would be set (visible to LSL, but not modifiable) that would cause the obect to de-rez when the last user has exited the vehicle. Also, an item rezzed in this manner would not count to prim usage on any plots.
In short, it simply becomes another form of "attach", but one that allows the same physics and script interactions that would occur if the item were directly rez'd by the user.