The short answer is you can't in the fcurve window, you can in the story tool if your clip is readonly and you cycle the clip...it will offset its self.
The Fcurve Hack: Do it by hand
- Use layers.. copy the forward translation keys,
- go to the end of the first cycle, the last key and paste on to a new layer, ignore the warning!
- In the fcurve window select the keys again and in the lower left..text box for the selected keys, type in 0- to move the pasted keys to start at a value 0 on the last frame of the cycle.
- For more offset cycles add another layer and repeat for your cycle.. the point is each layer will add to the existing one, so each pasted set of keys, you will offset in time your self and move the keys to start at 0 value on the time line at that point so that the layer does not effect the animation up to that time.