The Evil Cron Job that Won't Run

Hi guys,

so this is about a plugin you didn't write.... but i would appreciate any info you can give me.

I have a piece of software, which, for the sake of civilized language, we shall call My Presentation. I left out the expletives.

so this thing is supposed to send mails on schedule to attendees.
It uses a cron job to do so.
i tested the cron job on multiple servers all around, and the free / paid public cron servers are all running this effortlessly. even really well.

on my hosting with the crocodile company, i know their cron jobs also run.
but, no amount of calling the right version of php will make THIS script happen.

so my next question is - is there a gadget that i can use from wordpress, that will schedule a cron job for me, and that will not need it's libraries carted all over the known universe to get the executable to engage...

i look forward to your considered advice.