You can use Reason to record your mic & Reason sounds at the same time.
Do this by creating an audio track to record the mic, and another audio track to record the master output.
To avoid mixing the mic back into the master output, just route that audio track direct out to an unused output on the back of the rack.
What this will give you is your voice on one track, and your Reason sounds on another.
Since you can arm & start recording both tracks at once, they will be in sync when you import the wave files into CamStudio.