Depr.Meth: Sum-of-the year ascending numerical serie

Hi.

My client need a new depreciation key using sum-of-the-year method but using a ascending numerical serie. Thats mean the for example:

ACP = 1000 $

Useful live= 4 years.

Total remaining useful life: 10 (= 4 + 3 +2 +1)

Deprec. 1st year = ACP * 1 / Total remaining useful life = 1000 * 1/ 10 = 100

Deprec. 2nd year = ACP * 2/ Total remaining useful life = 1000 * 2/ 10 = 200

Deprec. 2nd year = ACP * 3/ Total remaining useful life = 1000 * 3/ 10 = 300

Deprec. 2nd year = ACP * 4/ Total remaining useful life = 1000 * 4/ 10 = 400

But, in SAP standard only i can find a similar depreciation method using Base Method 0001 (Ordinary: sum-of-the-years-digits) but this method use a degresive numerical seriefor depreciation calculation:

Deprec. 1st year = ACP * 4 / Total remaining useful life = 1000 * 4/ 10 = 400

Deprec. 2nd year = ACP * 3/ Total remaining useful life = 1000 * 2/ 10 = 300

Deprec. 2nd year = ACP * 2/ Total remaining useful life = 1000 * 3/ 10 = 200

Deprec. 2nd year = ACP * 1/ Total remaining useful life = 1000 * 4/ 10 = 100

¿Is possible customize a deprec. method sum-of-the-year method using a ascending numerical serie using SAP stander or i have to use a use a develop enhancement for depreciation method?

Best regards.