Replace all character matches that are not escaped with backslash

I am using regex to replace ( in other regexes (or regexs?) with (?: to turn them into non-matching groups. My expression assumes that no (?X structures are used and looks like this:

(
  [^\\]     - Not backslash character
  |^        - Or string beginning
)
(?:
  [\(]      - a bracket
)

Unfortunatelly this doesn't work in case that there are two matches next to each other, like in this case: how((\s+can|\s+do)(\s+i)?)?

With lookbehinds, the solution is easy:

/(?<=[^\\]|^)[\(]/g

But javascript doesn't support lookbehinds, so what can I do? My searches didn't bring any easy universal lookbehind alternative.