You can install a third party SSL certificate (wildcard or otherwise) on an IOS device if you have the private key used in generating the CSR. This is possible if you use openssl (or XCA if you prefer a Windows GUI - both are open source and free) and save the private key to a file so that you can combine it with the issues certificate and then import into your device(s)
The procedure is as described here:
https://community.cisco.com/t5/vpn-and-anyconnect/installing-ssl-certificate-s-on-ios/td-p/1527611
That said, it's generally not necessary. Even if you manage your devices using the Web UI and https you're already accepting a self-signed certificate to do so. Not much difference between that and accepting a self-signed EXPIRED certificate.