You'd have to at least increase the page size to allow 4kB of consecutive data without interfering with the page header.

OR you restructure the code and data to work around the page headers.

Or you could write a new SQLite VFS that somehow separates the page headers from the page data.

You still have row headers. Yes in the extreme you could write a VFS that parses the blobs out of the database and writes them sequentially somewhere, but it's much more practical to set the page size to 64kB and probably get 56kB of contiguous data in the middle of each page, then add padding into your blobs so that contiguous data is exactly the data you want to mmap