Have you discussed the requirement with the Finance department?
The fact that the customer does not wish to maintain condition records is not a particularly strong argument in this case.
Usually there is a good reason behind applying a 100% discount instead of using a non-pricing relevant item.
For example in some countries the customer does not pay the price of the free product, but still has to pay the VAT.
In another country if the company gives more than 49% discount, it should pay additional charges and this information should be reflected in FI postings (legal requirement).
CO department may also insist on having certain value fields updated in the FOC process, which they probably have now-based on KE4I settings. If you change the current approach, this would impact their reporting, so it is a good idea to speak with them as well.
If I receive such requirement from a SD key/end user providing only what you have shared as information in the post, I would also consider the possibility that he/she might be looking for a way to abuse the current setup and would not perform any changes before receiving approval from FI/CO and evaluating the additional reporting requirements for the other departments.