I imagine there would be a way to change the chunk separator format but a cursory glance at ?read_chunk does not give an obvious hint. The format actually used to be different IIRC, so probably a small request if not currently available (it would make sense, based on this example).
Edit: actually, the regex is hard-coded,
library(knitr)
.sep.label = "^(#|%|--)+\\s*(@knitr|----+)(.*?)-*\\s*$"
assignInNamespace(".sep.label", .sep.label, pos = "package:knitr")
Yihui might be open to a pull request to override the default.