I was hoping I could do it without needing seek(),

Why not just hide the seek inside a function of your own? Something like:

sub printAt {
    my( $fh, $src, $nChars, $offset ) = @_;
    seek $fh, $offset, 0;
    return print $fh substr $src, 0, $nChars;
}

printAt( $fh, $s, 4, 1234 );
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Actually, that's a good idea. The problem with that, though, is that the print function completely erases the rest of the file. Now that I think about it, I don't know if I ever found a good way to overwrite characters in a file without erasing the rest of the file...

The problem with that, though, is that the print function completely erases the rest of the file.

It won't if you use the right open mode; ie. '+<':

#! perl -sw
use strict;

## Open for reading and writing
open IO, '+<', 'junk.dat' or die $!;

seek IO, 11, 0;
print IO 'this overwrites';

close IO;

__END__

C:\test>type junk.dat
xxxxxxxxx
xxxxxxxxx
xxxxxxxxx
xxxxxxxxx

C:\test>junk59

C:\test>type junk.dat
xxxxxxxxx
this overwritesxxxxx
xxxxxxxxx
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