Can I can get / issue myself a cert for *.foo.com and update my DNS to point to Aptible?
Sure thing. When you add the wildcard cert bundle and private key, the ELB will provision and give you a hostname on an *.aptible.in domain for which you can add a DNS record.
However, wildcard certs won’t work for default VHOSTs (*.on-aptible.com) because Aptible uses it’s own wildcard certificate for these, and they are only good for one level deep; using the *.foo.com cert will fail if you try to use it for baz.bar.foo.com