This method may not suit you, since it does not capture the initial string, but it evades the string evaluation technicalities:

$ perl -le '$_=q(ab cdefg);s/(?<=\w)\b/,/;print;'

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This inserts a comma at the first word-nonword boundary in the string

After Compline,
Zaxo

In reply to Re: Interpolating $1 within a variable by Zaxo
in thread Interpolating $1 within a variable by s0ttle

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