A skilled corporate travel agent should probably tell you to pound sand.

Paying additional for exactly the same product would likely be a breach of most companies travel and/or ethics policies (for the person making the request), and certainly outside of what most companies would expect as a part of a corporate travel contract.

Requesting a higher fare class is potentially a different story as there may be different conditions/benefits available when doing that (be that the ability to upgrade, better chance of SDC, or on some airlines even things like the ability to select seats/priority/boarding/etc), but in this case you'd be asking to purchase *exactly* the same product at a higher price to the company.

(OK, so technically fare conditions can vary within the same fare bucket class - but other than things like international BE that's rare, and not what is being suggested here)