Dynamic Route 53 records for ACM certificate validation - amazon-web-services

Question

I have a Route 53 zone (example.org) with a few record sets (example.org, sub1.example.org). I also have an ACM certificate with DNS validation for the domains described by the record sets.
All of this is described in Terraform.
Currently for the validation to work I have to list all of the domain names in the certificate (domain_name, subject_alternative_names), the certificate validation (validation_record_fqdns), and the Route 53 records (aws_route53_record resources).
Is there a better, more dynamic way of doing this so if I want to add a new subdomain I only have to do so in one place?
I read about the for and for_each features in recent versions of Terraform but so far it's not trivial for me to use that in this case.
resource "aws_acm_certificate" "example" {
domain_name = "example.org"
subject_alternative_names = ["sub1.example.org"]
validation_method = "DNS"
}
resource "aws_acm_certificate_validation" "example" {
certificate_arn = "${aws_acm_certificate.example.arn}"
validation_record_fqdns = ["${aws_route53_record.example-validation.fqdn}", "${aws_route53_record.example-validation-sub1.fqdn}"]
}
resource "aws_route53_record" "example-validation" {
zone_id = "${data.aws_route53_zone.example.id}"
name = "${aws_acm_certificate.example.domain_validation_options.0.resource_record_name}"
type = "${aws_acm_certificate.example.domain_validation_options.0.resource_record_type}"
ttl = 60
records = ["${aws_acm_certificate.example.domain_validation_options.0.resource_record_value}"]
}
resource "aws_route53_record" "example-validation-sub1" {
zone_id = "${data.aws_route53_zone.example.id}"
name = "${aws_acm_certificate.example.domain_validation_options.1.resource_record_name}"
type = "${aws_acm_certificate.example.domain_validation_options.1.resource_record_type}"
ttl = 60
records = ["${aws_acm_certificate.example.domain_validation_options.1.resource_record_value}"]
}