I just did a Five Guys, and the one here in Podunk didn't have combos. Since they put so much emphasis on the ordering process, I'm not sure they'd allow it, even if you asked to make it a combo (with a regular-sized drink) after the fact. It would be nice, though; even when I order a plain little burger (no cheese) or a hot dog, I don't come in under reimbursement.
This MSC has Sonic shops where we can order items individually or as a combo. That surprised me since it reduces the opportunity for an upsell.
If your path dictates you walk through hell, do it as though you own the place. -unknown