Wildcard Names ACM allows you to use an asterisk (*) in the domain name to create an ACM Certificate containing a wildcard name that can
protect several sites in the same domain. For example, *.example.com
protects www.example.com and images.example.com.
Note: When you request a wildcard certificate, the asterisk () must
be in the leftmost position of the domain name and can protect only
one subdomain level. For example, *.example.com can protect
login.example.com and test.example.com, but it cannot protect
test.login.example.com. Also note that *.example.com protects only the
subdomains of example.com, it does not protect the bare or apex domain
(example.com). However, you can request a certificate that protects a
bare or apex domain and its subdomains by specifying multiple domain
names in your request. For example, you can request a certificate that
protects example.com and .example.com.
Source: http://docs.aws.amazon.com/acm/latest/userguide/acm-certificate.html
Unfortunately this is not possible/supported.