using dynamic patterns on the left hand side of case statement clauses

[scowles@ckhb.org]

i would like to use dynamic patterns on the left hand side of clauses in case 
statements.

i'm working in zsh current as of 3.1-91-g7595b22e on ubu 19.10.

the options set for this example are:
    setopt extended_glob
    setopt glob
    setopt no_no_match
    setopt no_null_glob

the code is:
    typeset -a a b c
    a=( one two three four )
    b=( 16 17 18 19 20 )
    c=( two 20 )
    vb=$'|'
    for d in ${c}
    do
       case ${d} in
           $( eval echo ${(j:${vb}:)a} ) ) echo "1 found it" ;;
           $( eval echo ${(j:${vb}:)b} ) ) echo "2 found it" ;;
           * )                             echo "did not find it" ;;
       esac
    done


but, when i run the code, the interpreter escapes all the vbars and forces the
entire lhs pattern to be a string.

does the case structure not allow this use case?  or am i just missing something
from not reading docs carefully enough?