In its infinite wisdom, the Camel Book says:

You may only interpolate expressions that begin with $ or @, because those are the two characters (along with backslash) that the string parser looks for.(p. 62)

Interpolation is extremely powerful but strictly controlled in Perl. It happens only inside double quotes, and in certain other "double-quotish" operations(p. 63)

So it seems that your solution is the only way.

CountZero

"If you have four groups working on a compiler, you'll get a 4-pass compiler." - Conway's Law