Syndicated facilities - calculation of utiliization fee with minimum amount

Dear treasury experts,

I'm working on implementing syndicated facilities for the following example:

credit line: 100M EUR with with appfront fee and utilization fee of 0.2% p.a. for drawings higher than 50M.

I've created a drawing of 70M and a utilization fee is calculated with an base amount of 70. That works fine so far, but what I would like to have is the utilization fee based on the difference between drawing (70M)  and the minimum amount of 50M.

Are there any solutions in customizing with a new condition type, which I did not come across so far?

Or if not possible in customizing, are there any exits to implement this calculation logic?

Thanks for your help in advance!

Innotech