There is not all that much you can do to improve your bass technique without a bass, HOWEVER you can really improve your musical knowledge.
I highly recommend you read everything you can on http://studybass.com it will help you understand the role of bass and what you are trying to accomplish.
Keep time to songs by clapping or tapping the beat with the radio or better yet a metronome. (its really important that you develop a sense of rhythm and time)
Learn to read notation, and more importantly the rhythms (study bass will introduce this to you, teoria has tones more info on it)
Learn what the different types of chords/arpeggios are and how they sound, you can do this with a keyboard or by looking them up on the arpeggio finder at
Invalid Link Removed (study bass will tell you what an arpeggio is and why they are important)
Start learning where notes are on the fretboard via charts (when I was in school and bored I used to draw a grid and put all the notes in it, as if it was a bass, then highlight the major scales, and cross hatch the minor scale) its not going to give you the muscle memory to play it but it will make it easier once you get your bass.
You can also take your bike to Sam Ash/Guitar Center and start trying out different basses in your price range (and some outside
) to get a feel for what kind of sound you want and more importantly which bass feels the most comfortable.
When you finish all that stuff if you are still bored with anticipation then go to
http://teoria.com and see what you can learn there as well. (this is more about general music theory and it will confuse the heck out of most people at first)
GOOD LUCK!
You can also always come back here with any questions you have along your bass playing journey.
