Some airlines will allow you to hold an award until you get the points, but not for a long time. I was able to hold an award on DL last fall for up to 72 hours. I needed 13K points, which I was planning in any case to transfer from my Amex account. In this particular case, I wound up changing the trip once or maybe even twice.

However, no airline will allow you to actually travel before you have the points. You have to get the points by whatever means - buying them from the airline, partner transfer, or getting your own travel to post.

American Express allows you to borrow 15K points if you have a gold card and 60K if you have a platinum. You can use them immediately. If you do not earn them back in the next 12 months, you have to pay 2.5 cents for each point you own. Amex also sells points for 2.5 cents, I think up to 500K per account per year.