I'm trying to keep all writes in local memory.

If you have S %A="""HI THERE"",!,#,33.33,"" "",$ZTIMESTAMP"

and you O 2 U 2 W @%A C 2 ZW ^SPOOL
^SPOOL(1,1)="HI THERE"_$c(13,10)
^SPOOL(1,2)=$c(13,12)
^SPOOL(1,3)="33.33 67016,59246.6188873"

It works just fine and the output is in the ^SPOOL global.

However, I'm trying to avoid writing to disk.

I can't find anything besides using the SPOOL device that will allow the use of the "@" indirection.