Adding fields conditionally to formail call?

    Does anyone have ideas how I can "stack" th3e fieds before I
    call formail. I'm trying to minmize the called formail processes,
    because I now do:

        :0 fh
        * flag1 ?? yes
        | formail -A "X-header1: value"

        :0 fh
        * flag2 ?? yes
        | formail -A "X-header1: value"

        :0 fh
        | formail -A "X-my: required"
                
        ...

    But I'd like to call formail only onece with all headers in variables,
    like this

        field1 = ""     field2 = ""
        :0
        * flag1 ?? yes
        { field1 = "-A \"X-header1: value\"" }

        :0
        * flag2 ?? yes
        { field2 = "-A \"X-header2: value\"" }


        # Call only formail once with all headers known
        :0
        | formail -A "X-my: required" $field1 $field2
                

    But, This doesn't work, see log below.Ideas?
    jari


procmail: Executing "formail,-A,X-my: required,-A,"X-header1:,value",-A,"X-heade
r2:,value""
procmail: Assigning "LASTFOLDER=formail -A X-my: required -A "X-header1: value" 
-A "X-header2: value""
Usage: formail [-bczfrktqY] [-D nnn idcache] [-p prefix] [-l folder]
        [-xXaAiIuU field] [-R ofield nfield]