First of all, if you're planning on drilling a hole to add a tone knob, you are obviously altering the look of the bass. If you plan on keeping it forever, not a big deal, but if you ever want to trade or sell it, that little modification will likely reduce the value of the bass.
If you want to avoid drilling a second hole, then you already have 3 great suggestions listed above, depending on how much (or if) you use your volume knob:
1. Get a concentric stacked pot
2. Get a push/pull or pot to use as a tone knob and on/off switch; or
3. Just convert the volume knob to a tone knob (this is what I did with my Precision Bass Junior, and I find that I don't miss the volume knob at all).
Whichever route you choose, one of the prior posts was correct about values: your pot should be 250K or 500K ohms (the latter will be slightly brighter when fully turned up), and your capacitor will be either .044uf or .022uf (the latter will be slightly brighter).
Have fun! That's a great bass you have.