Hey Eurail friends!

Does anyone know if it is possible to exchange a pass type, without first purchasing the 2nd pass type that you wish to hold?

My partner and I purchased 5-day Global passes, & as soon as we did, we went to book all our trains that we planned to take, and they were all completely booked up! (For some reason it only shows you actual availability on reserved trains after you buy your pass?) So we had to get flights around europe so we could meet up with our hotel bookings. We would like to instead get a One-Country 3 day pass, since we’ll still be able to use it when we get to Italy and train around. 

Problem is, I don’t have enough money available on my Credit Card currently to pay for both passes (eurail says their pass exchange works in a way where you have to first purchase the new pass that you want, and they’ll refund you the difference, with a 15euro service fee per pass)

Does anyone know any way around this? I feel so stuck. I emailed them last week to inquire and have not heard back yet :(