Use LLD macro as function argument in trigger expression?

[semue]

Hi there!
I've set up an ecosystem of hosts inheriting macros from their ancestors. These macros are used to configure trigger thresholds, as in the following trigger expression 1:

{Basic:LogSize.last(0)}>{$TR_LOG_SIZE_MAX}

So far, so easy. Now I'm also using low-level discovery to create trigger thresholds. Since zabbix 2.0.8 does not allow me to compare my item value to a low-level-discovered macro, I resorted to setting up item prototypes as a kind of proxy, as in trigger expression 2:

{Basic:Connection[{#CONNECTION_NAME},AGE].last(0)}>{Basic:MaxConnection[{#CONNECTION_NAME},AGE].last(0)}

, wherein the item MaxConnection is just a calculated item with formula

{$TR_{#CONNECTION_NAME}_AGE_MAX}

That's not beautiful, but it works. Now the really difficult part is to have the "0" in "last(0)" configurable by a macro. What I'm trying to achieve is something like trigger expression 3:

{Basic:Connection[{#CONNECTION_NAME},SIZE].delta({$TR_{#CONNECTION_NAME}_SIZE_MAX})}=0

but that just yields an error "Cannot implode expression". Trying to substitute the macro again by a low-level-discovered item (similar to trigger expression 2 above) also yields "Cannot implode expression".

Is there some way to have the arguments to trigger functions be generated by low level discovery? Again: I'm using Zabbix 2.0.8 (just waiting for 3.0.2 for the big upgrade...)

Best wishes,
Semue