grpavg for discovered hosts with templated checks?

[GeoffE]

(this is a question for Zabbix 2.4.6)

I'm trying to set up a group average for a cluster of hosts that we've added via low-level discovery. Thost hosts have various Zabbix agent checks added from the discovery template that look like this:

get_stuff[{HOST.HOST},foo,bar]

What I want to be able to do is set up an item on our aggregate "host" that does something like this:

grpavg["Discovered Hostgroup","get_stuff[{HOST.HOST},foo,bar]",last,0]

Obviously, this doesn't work - because it replaces {HOST.HOST} with the aggregate's hostname.

I've got a workaround, whereby the template has each host create kind of a "shadow copy" of the data, using a calculated value - with a static key:

Calculated: last("get_stuff[{HOST.HOST},foo,bar]",last,0]")
Key:  stuff.data

This lets me do this:

grpavg["Discovered Hostgroup","stuff.data",last,0]

And this works just fine. But it seems rather of an inefficient and hack-y way of doing it.

Is there an obvious method to do a group function on a templated check like that that I'm missing?

EDIT: I should clarify that the reason that {HOST.HOST} is in the templated check is because it is actually pulling from an ElasticSearch installation (running on another host entirely). The check passes the hostname as part of that.