OK, let's try to make it as silly as possible:

my $s = 'A3xyz45M98AB7Z9';

($t=join'',map{/\d+/g?$_.=':':$_}split//,$s)=~s/:(\d+|$)/$1/g;

print $t;
[download]

Now I'm looking for an even worse way to achieve it :)