Well you could download a cape mod, don't know how to install new mods to tekkit though, I still haven't figured that out yet, but really haven't tried many ways though. I'll post a link to an updated cape mod, and if you need an older version click on Old Versions and click on the version of minecraft you are using on tekkit.
Link: http://www.planetminecraft.com/mod/smp-capes/
I really think this mod is cool because you can upload custom capes instead of being confined to using capes created by others.
(update): I figured out that the file you need to put the .class files in to add additional mods, it is called modpack. To install mods that don't require putting files in the resources folder, go to .techniclauncher. Then the technic pack type you want's folder, which should be named after the type you want. After that go to bin, open modpack with archive program (such as 7zip or WinRARArchiver) the last thing to do is to put the .class files there and your done!