do works, to a point, as does require. However, neither will let inline code see the surrounding scope. The only way to do this is with a fairly risky eval:

use File::Slurp;   #!important!

my $blah = new SOME::Module;
$blah->start;

eval read_file('guts.pl');

$blah->end;
[download]

This is not recommended, partly because it's slow. Eval can be risky, too, so read up on it before choosing something.

It's easy to build modules, so I strongly recommend that as an alternative course of action.