Last year I opened a DAF at VG to make sure my VG funds were transferred over before EOY, to take a 2017 deduction. But I wanted the lower minimum grants at Fido (or Schwab). Today I called to verify that I could transfer it over, and how to do it. They assured me I could, and it seems very easy.
In case anyone else is looking to do the same, here is the process:
I opened a Fidelity DAF, and got an account #.
Then I went to my VG DAF, and submitted a grant request for the entire balance to go to Fidelity Charitable (the Fido Rep said to be sure to use the one with Tax ID 11-0303001), labeled the purpose as "Other" and put my Fido giving account name and acct number in the text box that appeared, to make sure Fido puts it in my account, and not their general fund.
I'll watch at VG for the grant to be approved and funds transferred, and then within a few days the funds should show in my Fido DAF. That is my only concern, that Fido would put it in their general fund, but I saved a copy of the grant request with my acct # as proof of intent, and have no reason to believe they wouldn't honor it.