Hello Joe,

IMHO it seems that the Perl includepath @INC contains mixed paths of both perl libraries. The old 5.10.1 and the new 5.14.2.
However, Perl is not able to resolve the dependency tho the module feature.pm, which must be located in some of the folders.
Depending on what version you will get by typing perl -v on the shell, I would give a try doing following things to get the do-release-upgradeworking.
Create a perl-file from which you will start the do-release-upgrade
i.e. UpdateMe.pl.
Depending on your perl version I would manipulate the @INC path accordingly.
In case of Version 5.10.1 :
We have to replace following paths in the @INC:
/usr/share/perl/5.14.2/etc/perl by /usr/share/perl/5.10.1/etc/perl
You can do this by simply manipulating the @INC. As the wrong entry is at the first place you can remove it by an shift operation and unshift the correct path.
Like this:

#adjusting the @INC
shift(@INC);
unshift(@INC,'/usr/share/perl/5.10.1/etc/perl'); 
#Call to your script
qx(do-release-upgrade);
[download]

In case your are running the perl 5.14.2, you got to replace all the other paths pointing to version 5.10.1. For this I would recommend some reg-expressions.
Or to keep it simple you can redefine the @INC by

@INC = ('/usr/share/perl/5.14.2','/etc/perl /usr/local/lib/perl/5.14.1
+','/usr/local/share/perl/5.14.2','/usr/lib/perl5','/usr/share/perl5',
+'/usr/lib/perl/5.14','/usr/share/perl/5.14','/usr/local/lib/site_perl
+','/opt');
[download]

But first make sure that those folders exists at all.

However, I am not sure if a do-release-upgrade is the correct answer to this issue - I have some doubts.

I am no ubuntu expert, but it should be possible to reinstall perl as 'ubuntu package' or rpm or something like that.
I guess this approach would fit more this Issue.
In case that ubuntu install scripts are perl based you can use the approach above eitherway.

I hope this helps.. :-)

Best regards

Tobias