The company policy seems to make sense - the company pays for the travel needed for work. Splitting up RT tix into two halves - do you do it 50%, company pays what a one-way would have been, etc., just puts too much variation in the process. Policies are made for the 99% of cases - there will always be exceptions. I would suggest you lay out the situation to your expense police and see what they can come up with. Though it's often easier to just still with policy rather than allow one-off exceptions - dealing with questions, approvals, setting precedent, etc., often isn't worth the savings.

As for the logic of airline pricing - I think that's an oxymoron.

What I would certainly not recommend doing is buying and expensing a one-way refundable ticket and then refunding it and buying a RT that you can use - that would be expense fraud. I suspect your company would frown on that.