How to implement Voucher partial redemption/returns?

Hi Experts

We have a business requirement for gifting that may require a voucher to be partially redeemed (similar to iTunes). The face value of the voucher will be reduced by the current purchase with the balance available in the next purchase. We cannot use the promo/serial voucher types.

Hope to hear from anyone who managed to implement something similar.

Thanks in advance to all, Gerry Silva