Outline : Credit the estate with client account deposit interest.
All income that comes into the estate must be linked to a source asset. However, the source asset can be hidden so that just the income from it appears in the accounts. For example, if you want to show interest on a client account you would have to first enter the client account as an asset of the estate and mark the asset as an income only asset (there's a tick box at the bottom of the asset setup screen). This will ensure that the asset does not appear in the printed accounts but is available to receive income. Now you've added the income only asset, you can receive the income in the normal way by right-clicking on the asset and choosing to receive income against the asset.