Req. to retain transferred from BU for an asset (at cost level)

We have a requirement wherein once a asset is transferred (interUnit) b/w AM BUs (say from US001 to US005), we want to retain the parent owning BU at the transferred asset level so as future accumulation depreciation/amortization (etc) transactions have this parent BU as a part of accounting string.  This is required as a part of elimination/consolidation at GL level.

Would you suggest any delivered means to achieve it. Delivered InterUnit accounting is working fine but it's not fulfilling this requirement. Other options would be to :

1) Utilize an unused ChartField as Trading Partner (and get it populated while transferring).