Leaving aside the eval bug, if you wanted to make this code work, that's what the use utf8 pragma is for (permitting utf8 chars in the script source). It's lexically scoped, so you'll want it in each eval, so you could prepend it to the source code.

#!/usr/bin/perl
use strict;
use warnings;
use utf8;

my $var_with_é_accent = 10;
print "var is $var_with_é_accent\n";
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works fine on my perl 5.8.8 system. Maybe this helps you in the short term?