As stated in the book, Conjuring kinda sucks. Yeah, you can get that sword, but it takes so long to whip up the spell, only to have the sword last for so long. It doesn't make much sense, when you can just go out and get that sword (or other item) cheaper and easier the old fashioned way.
So here's my idea.
The wizard creates in a safe place (home, laboratory, trunk of his car, etc.) a summoning circle (like the one in Harry's basement), this space is specifically set aside for one purpose... holding an item for later use. The circle is then linked through a lengthy thaumaturgical casting to a glove, which contains the spell. When activated, the glove summons whatever is in the circle to the open (gloved) hand of the wizard.
I could see this being extremely handy as it's not always convenient to carry around your Wizard's Staff, loaded gun, sword or what-have-you.
The way I'm thinking this would be accomplished is the glove acts as a once per session use Enchanted Item. The player would have to specify what item was in the prepared space, upon activation of the glove's enchantment, the prepared item is sent into the Nevernever to be pulled out again by the glove.
Any thoughts?