There's probably something I'm missing about your circumstances...
and this is, admittedly, not terribly elegant...
but -- as printf (referred from sprintf says (loosely paraphrased), don't use (s)printf when print would do.
So -- on the off-chance -- would this be acceptable? 
my $str;
my $val = 0.123456;
($str = $val ) =~ s/^0//;
say "\$str: $str";

[download]

Output: $str: .123456

Updateprintf caution added

In reply to Re: Can sprintf suppress leading zero for float < 1? by ww
in thread Can sprintf suppress leading zero for float < 1? by RotoValue

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