It is possible, as some people have said, to use "can" and have the meaning be clear.
An example where context is enough:
I can go to university, or I can not go to university. Those are my options.
Here "not go to university" is clearly a unit since it's contrasted with "go to university". But that structure could be extrapolated to a case with two different verbs, albeit with a little more ambiguity:
I can slog through university, or I can not have the career I want. Those are my options.
An example where emphasis/intonation is (almost) enough:
I'm not worried about the bungee thing. If I get scared, I can always not jump.
Also, in spoken conversation, one almost always uses "can't" for "to not be able to", which means that when you hear "can" and a separate, emphasized "not", it probably means "to be able not to".
It's also worth noting that the spelling is technically enough, because "cannot" is the normal spelling for "to not be able to", whereas "can not" is the normal spelling for "to be able not to".
But this is such a common source of errors, even among native speakers, that I wouldn't rely on it.
Finally, if you really want to clear up ambiguity, a very helpful verb is "choose".
I can go to university, or I can choose not to go.
If I get scared, I can choose not to jump.
I can choose not to do this thing.
If it's not directly up to choice, you could say "avoid" plus the gerund:
I can avoid doing this thing.
By the way, in colloquial speech of the current generation (25 and under), here's a common pattern of sarcastic conversation. It relies on context and emphasis for "can not" to be understood.
— "Just to let you know, I'm going to sing the Batman theme a capella for the next hour."
— "Can you please not?"
i.e., "Please choose not to."
Someone is smoking in the hall of an apartment building. Another resident walks by and is put off by the smell. She says without preamble:
— "Oh my God, could you not?"