Hello everyone! I found out how to use Caustic in Logic as an external MIDI device. I guess this would work on other DAWs and operating systems as well but I did this with OS X and Logic Pro.
First, you need a desktop version of Caustic, Soundflower installed on your computer and Logic Pro. First go to your system settings and choose soundflower as the main output device. Then in Logic create an external MIDI track and choose Caustic as an output and soundflower's stereo input as an audio input. Create MIDI sequences in Logic and set the sounds in Caustic. Have fun!