The obvious one is IBZ-FRA-LHR or LCY. Both have 2 seats. Leaves IBZ at 08:05. You can book that online in 2 bookings, or presumably ring up to see if they can merge into one booking (though the latter will almost certainly be more expensive since you won't be RFS). Alternatively IBZ-ZRH on Air Berlin, then overnight there for BA to London the next day. Also Basel is available. If Frankfurt is OK then I'd book it and then accept an amendment fee if the direct service comes up from IBZ or PMI. I imagine IB+ will have a few more options, but I haven't checked.

The other option for one person is IBZ-ALC-MAD-LHR, leaving IBZ at and getting to LHR at 22:10, almost longhaul in terms of impact! Also available via VLC.