Can you summon pets in passive?

Try reversing the order of the commands. The way the game reads multiple commands, it goes from the last to the first, so in that string, it's telling all pets to go to passive, then activating the summon.

Although, given that the summon is a location power, it's likely impossible to do, since the petcom will take effect immediately after you activate the power, but before anybody could click a location and actually summon the pets. So I'm thinking this probably won't work.

As for any other way of doing this, I don't know if there are any. Hopefully someone will come along and be able to help you.

No, this is wrong. The way the game executes powers, the last power in a bind will be executed first.

Consider:
powexecname POWER_A$$powexecname POWER_B$$powexecname POWER_C

The game first queues POWER_A. Then the game queues POWER_B, which pushes A out of the queue. Then the game queues POWER_C, which pushes B out of the queue. There's no more commands in the bind, so the power queue (containing C) is processed, and C executes.

Binds and macros are executed left to right. The power queue system forces multiple powers in a single bind/macro to execute right to left. The commands themselves aren't being processed in that order, though.

I can tell you that sometimes I try to summon my lost pets during a fight out of sight when possible . But I also want to upgrade them first before I send them back in.. Sometimes the pets will run in and attack and gain aggro before I can put them on passive. When I am successful though I can summon the pets and buff them without them getting aggro.

I notice that when fighting higher con mobs plain non upgraded pets just seem to get destroyed much faster.

I'm guessing the OP is trying to do the same..

I usually SPAM passive as I summon the pets and hope it works.