I'm going to be honest and forthcoming and tell you that it will cost you much more in time and/or materials to make what you have work, than to save the tube for a front-wired gun project and buy the right buffer tube for the job. It also depends on how deep the flange is, and only you would know that because none of us can see the tube on the inside.
So let me get this straight, you ordered some in-stock items from Depot, but since there is no notion of a real-time stock system, you were refunded for out-of-stock items, and now your funds are tied up. Yet you insist on buying there again because...the bunch of other products appear to in-stock?
Oh, I totally have about 8 spare buffer tubes in my personal stash as well. LOL
http://www.airsoftcanada.com/showthread.php?t=168219
Lastly, Stealth Top Tip - use a credit card when using Paypal for online purchases. Your funds don't get tied up and you can probably earn rewards/points on your credit card.