How can I set-up a leave sharing bank?

We have a new policy that allows donors, from their vacation accrual bank, to donate their hours to a shared sick bank.  Has anyone set something like this up and if so can you share with me how you do it?

We don't have a problem setting up the donation element which will pull from the existing donating employees bank.  But what about the set-up of a shared bank and the ability to put the hours into the shared bank as well as  allow another new element for the receiving employee to take from the shared bank?

Monica