A better idea would be to do something like this:

package Foo;
use vars qw/$delHook/;

$delHook = undef;
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Export $delHook if you like. Then, in the main script:

$Foo::delHook = \&somehook; # or just $delHook if exported
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will set $delHook; in the module, when you need to call the sub:

$delHook->(any_arguments_here) if defined $delHook;
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That way, rather than being restricted to calling a sub with a particular name, you call the subroutine by having a reference to it (which is what the \ does; the & is just to specify that it's the method and not something else). Note that the call will not occur if no delHook was set.