How can burdening be implemented for a grant where burden rate is determined based on funding amount

Summary:

I have this scenario for Grants where overhead costs/burdening needs to be implemented based on funding received. Need help on this.

Client take their funding and DIVIDE BY number of months for that grant is. So, for example there is a Single Year Grant which has 1000$ for a year, so they will divide 1000/12 which is 83.33 per month. They charge the grant and credit the operating income for the college each month. It is a sweep to the operating revenue and a charge to the grant.

Not able to understand how standard functionality can be used, as the percentage would differ every time as per the Grant funding, also would differ by each budget Period if the amount received for a Multiyear Grant is not constant.