I'd do it like this:

The INI

[GENERAL]
scheduledb=something
[SERVICE]
start2=stuff ${GENERAL/scheduledb=default} etcetera
[download]

The "getter":

sub x_val {
  my ($ini,$sect,$key,$def)=@_; # same signature as 'val'
  my $val=$ini->val($sect,$key,$def);
  my ($sect1,$key1,$def1,$t);
  while ($val=~/\$\{([^}]+)\}/) {
   $t=$1;
   ($sect1,$key1,$def1)=($t=~m|^([^/]+)/([^=]+)(?:=(.*))?$|);
   $val=$`.(x_val($ini,$sect1,$key1,$def1)).$';
  }
 $val;
}
[download]

Notes:

• It uses pre- and post-match variables, so it will slow you regexps
• The syntax is a bit different from the one you show
• It expands recursively
• It supports in-line defaults
• I haven't tested it...

-- 
        dakkar - Mobilis in mobile