I spoke to my senator and showed up at the meeting briefly, and successfully got a "best of both" scenario going.
$300 will be in a ASUC Events fund - spendable by reimbursement only, reimbursed after the event, with the full limitations.
$150 will be in the LCS account itself, spendable by normal ASUC restrictions (no food). Not sure if this part is restricted re honoraria etc. Any printing has to bear ASUC logo and state wheelchair accessibility (it is).
This means that the LCS is now a ASUC sponsored student group, which means that we will have an ASUC account and be able to accept donations via the ASUC's nonprofit tax ID. Also removes most of the weirdness/complications from the previous (allornone) scenario I outlined). All donations go to the LCS itself, spendable as decided (NSA) - much easier to deal with. Wouldn't even need to be reimbursement-only AFAIK, since it's "our" money we can spend it as desired. Dunno if I can write checks directly on the LCS account though; probably not, but I'll find out.
I'll need to have a meeting with one of the other signatories and the ASUC finances person to go over how accounts work, how to take donations, etc; will update when I know that procedure.
Still waiting on the outcome of the second grant request.
One issue though is that the $450 *is* reimbursement-only money, and $300 of it only can be reimbursed *after* the conference. I'm not really flush enough to be able to just take that debt on myself comfortably. :-/ So, I'm not sure what to do about it. This would be even more so if it turns out that LCS funds are also reimbursement-only; it'd leave me having to carry debt while the reimbursement process goes through, and probably from my checking account rather than credit - which isn't really practicable.
I'll have to bring this up with our financial advisor and see about the pragmatics of it, but if it's feasible on my end - anyone willing to loan the LCS a few hundred for a couple months - just long enough for the event to finish and reimbursements to go through? I have no idea how this would work though; not sure if it'd be more juggling than it's worth.
FWIW: I've gotten several offers of donations lately - thanks! Pledged donations so far total $635. That puts us definitely within reachable range of at least breaking even. I'll be updating everyone with details on how to send the money (and get tickets in advance) soon.