If you were in a single degree, i'd suggest taking them as a general elective rather than science elective. 99.9% sure when you pick up a double degree you sacrifice the ability to take electives outside your double field to save time though. If worst comes to worst, i believe it is possible to enrol in a "subject without credit" or something like that. It wont count towards your degree or anything like that. It is a bit hard though since your degree (and the government) is only approved for and will only usually pay for X number of units. Inquire about this if it does come down to it though.
Thanks for the advice

I am in a bit of a strange double degree; biomed greatly restricts the majors available to me for the BSc, and you're correct in saying that I don't get non-science electives. Apart from the issue that I have in not categorising HSCxxxx units as science, I've got a slight problem resulting from my major selection. Because of prohibitions, I don't get to actually take any GEN/PHY-prefixed units until level 3; there are (compulsory) exemptions in biomed for the level 2 units.
So, I'm left with 4 empty places for BSc units next year; I've filled up two of them by taking DEV2011 and 2022, and I'm pushing for the HSC units a) because they're interesting, b) because they're relevant to my preferred career pathway and c) They're run the HSC units in Caulfield, where I live (what up, convenience!).
After speaking to the sci enquiries people today, they told me that HSC2111 and 2141 used to be allowed as science units way back in '10 and '11 and they didn't know if anything had changed; I can't take 2141 (due to biomed prohibition), so I was advised to enquire about taking 2111. I also found 2102 in the handbook and I'll be pushing to gain entry to that unit because it's ridiculously valuable from an education perspective.
BLEGH this is so difficult