Since Gandalf was a wanderer and he brought fireworks with him all over Middle Earth--I have come up with a new suggestion to help with this endeavor.
When Gandalf is able to mount, instead of immediately showing a mount/shadowfax, a cart appears. The cart would function like Sauron's Tol-in-Gaurhoth in that Gandalf selects the cart and places it on the ground somewhere.
Once this is done, the cart becomes like a mini building with the following options:
1. Detonate like an Isengard Mine but with beautiful colors.
2. Changes Gandalf's powers to reflect his Erebor persona as we have stated earlier.
After Gandalf drops the cart, he may then mount/dismount. Now if his cart is destroyed then he must either mount or dismount to get the cart to appear on his palantir again.
So essentially Gandalf can place the cart around like Sauron's Tol-in-Gaurhoth, but the power has a feeling like Witch King's mount--that is to say like the Witch King can switch between horse and fellbeast, Gandalf will be able to drop his cart somewhere and then mount or dismount.
What do you all think of this idea. I still don't think Gandalf would be OP from this.