Hey Juan,
Using vCAC designer, which is a basic designer, you cannot convert the vCO workflow to provisioning Workflow only you can call the vCO workflow using custom option in already existing 10 workflow. However if you call your vCO workflow and that vCO workflow has some required input parameters which needs to be provided while workflow initiation, is not possible in this scenario because this call method does not pass input parameter filed to vCAC portal for user intervention.
In order to get it working, you compulsorily have to provide all input parameter at workflow modification level. Which is no fun of just clicking a button and see machine provisioning with pre-populated parameters.
To get workflow be working from vCAC as desired, I guess you need cloud Development kit license.
Br,
MG