Yes, you can send Aetna secondary claims electronically!

Since we support the HIPAA standard for electronic batch claims submission, we accept electronically submitted coordination of benefits (COB) claims. You can submit COB claims directly from:

• A provider who has received a remittance advice from the previous payer (provider-to-payer COB)
• The previous payer (Payer-to-payer COB)

Not sure what’s needed to send in an electronic COB claim? These tips will help you with what’s required and alternatives, if your practice management system or clearinghouse isn’t COB-ready.

http://www.aetna.com/healthcare-professionals/claims-administration/electronic-claims-tool.html