I don't fully understand what you mean. You can simply 301 redirect all post URLs to the corresponding topic URLs:
Activate the "No duplicate" & the "Zero duplicate" options (Strict Mode: No, Posts Redirections: Guest or all).
This option will determine how to handle post urls; it can take four values :
off, do not redirect post url, whatever the case,
post, only make sure postxx.html is used for a post url,
guest, redirect guests if required to the corresponding topic url rather than to the postxx.html, and only make sure postxx.html is used for logged users,
all, redirect if required to the corresponding topic url.
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