You can do what I do - USB/Serial module, and DIP chip, emulating a Duemilanove.
I can't really speak to what the OP wants - but I think what's being asked is whether there's a way for the Uno to act as a USB HID device like the Leonardo can.
If so - the short answer to that is "yes and no".
I do know that in the past there were people playing around with shields on standard Arduinos, plus code that allowed them to use an Arduino to emulate a keyboard or a mouse; if you google "arduino usb hid" you'll find a myriad of resources and such discussing how to do this.
That said, you'll likely have to do way more programming and such than you would have to when using the Leonardo - but you might gain a better appreciation and understand of the whole process in the long run. Also - more people seem to own, use, and discuss the Uno (and other 328 based boards) than any other Arduino system. In fact, the number of people using these other Arduino systems seem to be of a much lower number - so it may be more difficult to find help and/or example code. I'm not saying impossible - just more difficult. They just don't have the same popularity.
Also keep in mind, though, that since the Uno doesn't have this built in rather "natively" and you would have to code it in yourself, that code might take up such an amount of space as to leave you little room for your own code; I honestly don't know what the truth is on that side of things, though, since I haven't played with USB connectivity, but it is something to keep in mind as you do your research. I would imagine that the Leonardo, with it's more "native" handling of USB HID, might have simpler and smaller code needed to implement it.