Hey, look at that, someone having the same issue as me! :) I, too, mourn the loss of Latitude. It just worked. I've made some progress, but I don't think it's possible. Specifically, while watching the logs while switching to it, I found that they're launched using the activity com.google.android.apps.plus/.locations.FriendLocationsActivity. This one appears to not be launchable by other apps.
If I run:
am start -a android.intent.action.MAIN -n com.google.android.apps.plus/.locations.FriendLocationsActivity
I get:
Starting: Intent { act=android.intent.action.MAIN cmp=com.google.android.apps.plus/.locations.FriendLocationsActivity }
java.lang.SecurityException: Permission Denial: startActivity asks to run as user -2 but is calling from user 0; this requires android.permission.INTERACT_ACROSS_USERS_FULL
This indicates an issue since 4.2 which added multi-user support. However, if I run it with the "--user 0" switch, we get:
Starting: Intent { act=android.intent.action.MAIN cmp=com.google.android.apps.plus/.locations.FriendLocationsActivity }
java.lang.SecurityException: Permission Denial: starting Intent { act=android.intent.action.MAIN flg=0x10000000 cmp=com.google.android.apps.plus/.locations.FriendLocationsActivity } from null (pid=981, uid=10155) not exported from uid 10206
Which is also normal. The way I've worked around this in the past is to run the am command as root and typically it fires the app right up the way I want. If I run the command as root, it DOES launch Google+ directly into the Locations screen, however it constantly asks me to turn on Location Sharing (which is already on). If I click "Sure, turn it on", I get a toast that I'm not signed into Google+...almost as if it were running as a different user. :) I did try launching the app directly and then calling the activity, thinking it might just reuse the already running app, but no such luck.
So, if anyone can expand on how to work around such limitations, hopefully they'll share. One other item I'm thinking of just now...when Google moved Locations into Plus, a lot of folks using custom ROMs had issues. It would show an image of the people on the screen, but no map under them to make it useful. The only workaround was to make Google+ a system app and move its libraries into system, too. There is the possibility my having done that is exacerbating the issue, so you might want to try the above steps if you're running a stock ROM. Another option I've seen, but am no interested in trying, is to move Tasker to /system/app. Typically, apps that don't export some activities will allow system apps to run them. Might be an exercise worth trying someday, but not in the mood to do it anytime soon...
-T