To first clarify, the transaction would actually be a Rollover, whether it was coming from the 401(k)or go to the 401(k). Transfers can only be done from the same type IRA to IRA.
It would then mostly depend on your custodial agreement with the IRA owner and whether the Qualified Employer Plan allows it. Normally the IRA owner would consult with the plan administrator to determine whether it can allow the transaction, as we should not give that type of advice.
Hope that helps....a little late.
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Nothing changes, if nothing changes. (from a good friend of mine)