Yes it is possible. In config setup, set "nat_traversal = yes" at both ends. You will also need to play around with the left/rightid. The nat'd ClearOS (if it is left) will transmit a leftid of its LAN IP, so at the other end (your server) you'll probably want rightid=your_friends_LAN_IP, or perhaps it is better to override it at both ends with something like leftid=@myfriend and rightid=@Eli. I would assume you are using PSK's so make sure the ipsec.secrets file has a %any keyword as both WAN IP's are unreliable - or you have to read the secrets file each time one WAN IP changes.

For your friend, port forward udp:4500 to the LAN ClearOS and open udp:4500 on your server.

You'd do best to use your poweredbyclear.com FQDN's as these generally update and propagate through the DNS system quicker than things like DtDNS.

If either of your IP's change and you are running IPsec on the gateway you can try using dhclient-exit-hooks to detect an IP change (i.e not just a DHCP renewal) then fire off the command "ipsec whack" of, if you're using PPPoE there is another file, /etc/ppp/ip-up, which you can hook into instead - or, I believe, just create a file /etc/ppp/ip-up.local with your script in it.

[edit]
I forgot to add, on the 5.2 machine you'll need to add a static route to your own server via your friend's 7.x machine.
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