The easiest way is to use pkgrecv to pull the package from a source repository to a local repository. IPS is a network package system so you can't currently install packages from a single file like you could with SVr4 datastreams. Last I heard (before the Oracle takeover) was that the pkg5 guys were working on an on-disk format but I don't think it got finalised. I can check with one of the developers if you like though. Anyway, that's by the by.
What you need to do
Create a local package repo:
pkgrepo create /path/to/localrepo
Grab packages from remote repo:
pkgrecv -s http://pkg.openindiana.org/dev -d /path/to/localrepo <FMRI_or_glob_of_packages>
It's been a while since I did this (last time was when OpenSolaris was on the verge of shutdown and we [OpenIndiana team] were grabbing packages from OpenSolaris /dev) but you might need to set the publisher of your local repo to be the openindiana.org publisher:
pkgrepo set -s publisher/prefix=openindiana.org /path/to/localrepo
Start a pkg.depotd instance so that pkg can use it:
pkg.depotd -d /path/to/localrepo -p 10000
(You probably want to set this up in SMF. Follow the howto on the OpenIndiana wiki.)
Then add your local repo as an origin of openindiana.org:
pkg set-publisher -g http://localhost:10000 openindiana.org
And finally...
No, there really isn't an easier way of doing this. This is one of the reasons I don't like the move to IPS.