If you're going to write normal Perl, write normal Perl. If you're not going to write normal Perl, make it look like it isn't normal Perl.
With source filters you can do what you're asking for. However your maintainance programmer will (or at least should) hunt you down with a blunt weapon. But consider something like this which has (modulo syntax) the exact same structure as your program:
\nEND {\n # This is executed last, even though it appears first.\n print "This test checks that widgets can mate with thingamaboobs\\n";\n show_plan();\n do_plan();\n}\n\nplan(\n "create a gray widget",\n sub {\n ...\n }\n);\n\nplan(\n "create a red thigamaboob",\n sub {\n ...\n }\n);\n\n...\n\n
This is easy to implement, does what you're asking for, and it is fairly obvious to the maintainance programmer how the magic works.
Incidentally if you're doing automatic unit tests, is there a good reason not to be using Test::More? Perl has good facilities for such test suites, you just have to use them. (Ignore this comment if the point of your test suite is to have someone look at the screen and manually review that what shows up matches what was supposed to show up.)
Cheers,
Ben