As far as I know this can not be done in InDesign. If you export as spread the every spread will be treated as a single page in the pdf.
You have a couple of options:
1) you can export as spreads using the regular pdf export (PDFExportPreference.exportReaderSpreads)
2) If you export as an interactive pdf, you can set InteractivePDFExportPreference.pdfMagnification to PdfMagnificationOptions.FIT_WIDTH and InteractivePDFExportPreference.pdfPageLayout to PageLayoutOptions.TWO_UP_FACING or PageLayoutOptions.TWO_UP_COVER_PAGE_CONTINUOUS
There is also an option in Acrobat Pro to set how a PDF is initially opened.
Yeah. But he wanted to do it automatically in InDesign...