I've set up a node on my network that talks to the internet and runs 24/7.
If I need armory on a second pc on my network I setup bitcoin cleint to -connect=192.168.x.x in the bitcoin.conf. This means the additional node only talks to my node and no other nodes. So it only uses internal bandwidth to sync up.
The diskspace is still wasted but at least I could move the additional node to online quite easily if I wanted to.
I wouldn't do this on a laptop though as the 192.168.x.x could point to any pc if you connect on another (untrusted) network.
That's a good way, yes.
I did that in my android bitcoin wallet (Schildbach), setting the trusted IP to the node in my LAN. Saves bandwith and sync time. It's just a static additional IP though, so my wallet connects just fine too when I'm on mobile.
Ente