I'm not sure about the availability of different ground leads for the Rigol probes. In all cases though, you really want the ground lead to be as short as practically possible. The importance of this goes up as the frequency of your signals goes up (or as your risetime gets shorter). For best signal integrity in the scope, use the shortest ground lead possible. Extra ground lead length adds inductance the ground path resulting in ringing and distortion of high speed signals - not to mention how increasing the loop area between the probe tip and ground will increase the amount of noise the probe will pick up.
In the short term, if you can't find a suitable ground lead and clip, solder a short length of bus wire to the ground pin of your ICs (if possible) and attach the clip to that. You can unsolder it when you're done. For high speed circuits, wrap your temporary ground wire around the coaxial ground shield adjacent to the probe tip to minimize the ground lead length and loop area.