Sorry, I misread your problem...
Is the header always of a fixed length in terms of the number of lines? Or can you easily find out from the file how long the header is? If so, you could first read just the header and, instead of using spreadsheet to array function, you could parse the header yourself by using the match string function in a While loop with the search value:
[\s\t]+
Assuming slash codes are enabled, this string will match any string of one or more spaces or tabs.
You could then read the rest of the file and format it using spreadsheet to array with the tab delimiter (that is constant, correct?).
If you need help with that parsing loop let me know and I'll write one for you...
Mike...