Fortigate certificate management via ACME - not using Let'sEncrypt !

Hi,

Would like to manage the web-server certificates automatically for some Fortigates using ACME protocol connecting to an internal PKI ACME server. As far as i can see, there is only the option of connecting via ACME to Let's Encrypt. 
Is there any option of using ACME via Fortigate but using a custom ACME server? 

Othewise, will have to create a custom script to manage the certs leveraging FortiManager/FortiGate API. 

Thanks,