A 100kB view will not help you truncate from the front. You can use it to copy chunks like mcduff suggested but
The issue with what the OP is asking is to get the OS to recognise a different start of a file. Truncating from the end is easy (just tell the file system the length has changed). From the front is not unless you have specific file system operations. On Windows you would have to have Sparse Files to achieve the same as fallocate