Problem defining factorial operator in .rakumod file

[Joseph Polanik]

I am trying to define '!' as the factorial operator. The following works 
in a .raku script file:

  sub postfix:<!> ($n) is export {
    when $n == 0 {return 1}
    default {$n * ($n - 1)!}
  }
However when I tried to move this sub to a .rakumod file, it produces an 
error: Negation metaoperator not followed by valid infix.

It turns out that this is a known issue, #3774,  with rakudo first 
logged (AFAIK) in July 2020. Until this is fixed in some future release 
of Rakudo, is there a workaround for this?

Note: I am using Rakudo v2022.07 on Ubuntu 20.04.5.

Thanks,

Joe