Gary,
Labview provides you with a great deal of power in customization. Rather than an other VI, you can simply edit the 2ch scope.
If you open the diagram to the 2scope aquire VI you will notice that the time base selector indexes an array of values which are being sent the the AI Waveform VI. If you modify the values in this array you can achieve the timebase you want.
Note that valid timebases will be limited by your daq device.
Regards,
Amaury R.
-NI Applications Engineering