The only way I could think of is to email them to yourself in the form of a text message. A lot of ringtone software out there enables a function that will text message your phone the ringtone you create. Xingtone Ringtone Maker is one of my favorites and I've had the best of luck with it. Make sure it's compatible with your phone(s) before purchasing it.
I basically just asked the same question. I emailed mine via email@example.com (make sure you have a pix account, is free), but... it puts then in "My Sounds", but I cannot figure out how to, if even possible, to then use them as ringtones or for contacts. Have you figured it out?