To be fair from the start you aren’t exactly going to use dyndns custom, but you will be able to make custom hostnames with your personal domain by using free dyndns services.
First of all you need tow free accounts, one for dyndns.com and the other for editdns.net.

Next up is setting your name servers to editdns. To do this you need the use the method your registrar provides and to point your nameservers to: free02.editdns.net and free01.editdns.net. This ensures that you can manage your DNS as you please, when you please. (Make sure you set up the A and MX records asap, you don’t want your website and e-mails not working.)

Now for the DynDNS part. Just add a new, free, dyndns host. I know it says “add to cart” but it costs $0,00, so no worries. You need to ensure that the hostname updates every time your IP changes, for that you can use the client dynDNS so generously provides.

And the final step. Go back to editdns and add the following entry:
Record Name: host.domain.com (the hostname you want people to use, for example dad.myfamily.com).
Type: CNAME (this means the hostname is actually an alias for another host).
AUX: 1.
TTL: 3600 (so that it drops the cache quicker and your hostname updates faster in case the ip changes).
IP/Host: host.dyndnsdomain.com (the actual hostname you’ve set up with dynDNS and the one that the client updates).

So that’s about it. It’s easy and mostly safe. Of course $29.95/year for a custom DNS service isn’t that much, but if you’re a student like me, you’d rather spend that on beer.