o rings are not compatible with my keycaps, any cheap replacement recommendations?

[GameableXP]

Here is a picture of my keycaps on my Rosewill RGB80:
http://imgur.com/INIFjc4

As you can see, the bottom is not circular unlike normal keycaps, so I can't install o-rings on them. So, I am asking you guys to list some cheap recommendations so I can install o rings on my keyboard. Here are some more pictures of my keyboard: (The keycaps are black and the letters are see-through)
http://imgur.com/eQCAIRU
http://imgur.com/AuNkxMk
(sorry about the quality of the pictures)

 

[ulises314]

Dental rubber bands, the ones they use with braces.