Dusted off the cobwebs, and I think I remembered how to do this:
{{{
koji add-tag f22-kde --parent=f22-build --arches=x86_64,i686,armv7hl
koji add-target f22-kde f22-kde
}}}

Ticket needs to remain open until we merge the builds in and remove the target

builds tagged, target removed.
{{{
$ ./mass-tag.py
Checking 31 builds...
Tagging bluedevil-5.2.0-1.fc22 into f22
Tagging kde-cli-tools-5.2.0-1.fc22 into f22
Tagging kde-l10n-4.14.3-3.fc22 into f22
Tagging kdecoration-5.2.0-1.fc22 into f22
Tagging kdeplasma-addons-5.2.0-2.fc22 into f22
Tagging kf5-baloo-5.6.0-1.fc22 into f22
Tagging kf5-kfilemetadata-5.6.0-1.fc22 into f22
Tagging kf5-kwayland-5.2.0-1.fc22 into f22
Tagging kf5-modemmanager-qt-5.2.0-2.fc22 into f22
Tagging khelpcenter-5.2.0-1.fc22 into f22
Tagging khotkeys-5.2.0-1.fc22 into f22
Tagging kinfocenter-5.2.0-1.fc22 into f22
Tagging kio-extras-5.2.0-1.fc22 into f22
Tagging kmenuedit-5.2.0-1.fc22 into f22
Tagging kscreen-5.2.0-1.fc22 into f22
Tagging ksysguard-5.2.0-1.fc22 into f22
Tagging kwin-5.2.0-3.fc22 into f22
Tagging libbluedevil-5.2.0-1.fc22 into f22
Tagging libkscreen-qt5-5.2.0-2.fc22 into f22
Tagging libksysguard-5.2.0-1.fc22 into f22
Tagging plasma-breeze-5.2.0-1.fc22 into f22
Tagging plasma-desktop-5.2.0-3.fc22 into f22
Tagging plasma-milou-5.2.0-1.fc22 into f22
Tagging plasma-nm-5.2.0-2.fc22 into f22
Tagging plasma-oxygen-5.2.0-2.fc22 into f22
Tagging plasma-systemsettings-5.2.0-2.fc22 into f22
Tagging plasma-workspace-5.2.0-1.fc22 into f22
Tagging plasma-workspace-wallpapers-5.2.0-1.fc22 into f22
Tagging polkit-kde-5.2.0-1.fc22 into f22
Tagging powerdevil-5.2.0-1.fc22 into f22
Tagging sddm-kcm-5.2.0-1.fc22 into f22
Tagging 31 builds.
Tagged 31 builds.

$ koji remove-target f22-kde

}}}