"Forgetting" to attach high school transcript

A big global firm (think BB/MBB/Big4) is hosting a fancy 2-day workshop on M&A for european students and I want to apply for a spot. The application form differs depending on what country you are from, and in my case (small european country) they ask for resume, cover letter and transcripts from high school and onwards. My problem concerns the last requirement, because while my GPA from university is good and my resume & cover letter-writing skills are fine, my high school grades are somewhat poor (compared to the grades of the type of people I know will apply as well, they're downright terrible).

A bit of background: In my country, HS grades generally matter way less than in the U.S and when applying for college (our college-application system is completely different to US system) HS GPA doesn't always matter (it didn't in my case, which is why I took the opportunity to slack off massively in high school)

So my question is: When I apply for this workshop, should I in my application include my shitty HS grades and hope they aren't a deal breaker OR should I "forget" to attach them? With the latter I obviously risk giving the impression that I can't follow simple orders - on the order hand the country-specific application requirements are only stated once on workshop's website and could easily be missing.

Advice is much needed (and appreciated). I realize I'm making a big fuss about a 2-day workshop, but 1) the issue may come up again in the future and 2) it's a sweet workshop :-) & barring my HS grades, I'm pretty confident I can get a spot.

Note: I'm assuming that it would be a bad idea to email firm HR to ask if it's OK if I don't include my HS grades, since my dog ate the transcript...