I'm sure you know it doesn't matter how many MILES you fly, to complete a Challenge; it matters how may POINTS you earn.

I'd recommend you purchase a lower fare you bill your client, upfare to a fare class that gets you past a Platinum challenge, and of course use the tools at hand to select flights and use miles and copay to upgrade at least the redeye transat flight so you can arrive more rested and able to do business.

There are other ways to get to MRS, of course, one of them using AA to MAD and IB to MRS (as you are doing for the return) or even using Thalys from CDG/Paris to MRS.

Obviously the only way to assure J is to buy it - but even I class is not looking useful this close out.