Sales order with Budget Availability control

Hi

We use Project System with budget availability control activated, which works absolutely fine with MM Procurement process. 

Now the requirement from business now is to validate the costs  for promotion (sample, free of charge goods,...) at Sales Order level within SD by setting  budget against WBS element and assign this WBS element in Sales order line item, rather than Good issue timing,

I am fully aware that there is no standard functionality within SD module for Budget Availability control, however, this should be a pretty common requirement and wonder if any of you would be willing to share a possible solution that you might have implemented or provide some good pointer that I might need to look at.

Thanks in advance for your expertise.

Kind regards

Taro