Connect existing EC2 nodes that are not in any VPC to the Jenkins controllers within the CJE infrastructure which is in VPC.
CloudBees Jenkins Enterprise (CJE) - AWS
Customization of the VPC settings does not currently suppurted beyond what you can enter in the initial configuration file that is explained in AWS-Specific Configuration Attributes.
You need to use JNLP agents for the connection of external nodes to CJE that it will connect them to the Jenkins master or declare them as shared JNLP agents in CJOC.
In order to be able to use JNLP agents, you have to open JNLP ports on the workers to those EC2 agents. If you can not open the JNPL ports for each IP address, then you can either recreate the cluster or put those JNLP agents within the VCP.