There is, using the MARK and JUMP keys. Assuming you have a lot of samples to assign and you have made up a program with sufficient keygroups, go to keygroup 1 and press MARK/#. Now move the cursor to the sample assign field below and select the first sample you want to assign to that keygroup. Now press JUMP/. This will take you to the KG field again and you can select KG2. Now press JUMP again to toggle you back to the sample assign field and select your next sample, press jump, new keygroup, jump, new sample, etc... Once you get some practice, you can assign the samples to quite a complex program in no time at all.
Another quick method for selecting keygroups method is to press and hold the EDIT key and play a note on the keyboard. This will select the keygroup for that note.
Please note that for either method, if you record (or load) your samples in the order they are to be assigned, then the process is even quicker.