I doubt Fdev will release a dev tool to their game for this purpose. For the moment though, try out Voice Attack (VA)! It's 10USD on their
website or try it for free first then make your purchase. This will get you started into making your own COVAS and voice assistant. All you need after that is a voice recording app/software and then import the sound files into the VA commands when needed. I've even used Amazon Web Service's (AWS) Polly app to make custom voice responses for my VA profile, for the free (up to 1 million characters, I believe). You can also use your default OS's speech engine(s). Also you can use this program for any other game (EULA pending, of course)!
There are many tutorial videos on YouTube and several
threads in these forums to show you how to program your commands and feedback responses. So don't be scared to hit the guys up in the threads for help!
I also suggest trying out the
EDDI companion app for VA. It provides more information and some better automation using the game's player journal entries. You can find help for that as well in the forum linked above. You can't really use your custom voices for this app (yet, or as far as I can tell) but many have used the EDDI app as a second "personality", so-to-speak for their cockpit.
Hope this helps, CMDR!
NOTE: Other voice packs (for VA) can be bought on this site:
HCS Voice Packs which features celebrity voices like
Will Shatner - Orion Pack and
Brent Spiner - Vega Pack