You could try using an expression to change the output of the cell when the RenderFormat is excel, to include either a leading apostrophe (single quote) OR an equals sign followed by the value wrapped in double-quotes.
e.g. = iif(Globals!RenderFormat.Name = "EXCEL", "'" & Fields!MyField.Value, Fields!MyField.Value)
This will then format your value differently for output to Excel.
However, I think how well this works may be dependent on what version of Excel you use - on my Office 365 version, it displays the leading apostrophe until you edit and save the cell, when it then displays correctly, which is not what you want, but you may be luckier.
MM
select geometry::STGeomFromWKB(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