After googling substantially before hand I stumbled across a blog linked to a codeplex sample. Trawling thorough that I got to

EXECUTE SQL TAsk contains:

declare

@startLSN binary(10),

@startLSN_str nvarchar(42)

select @startLSN = sys.fn_cdc_get_max_lsn()

select @startLSN_str = upper(sys.fn_varbintohexstr(@startLSN))

select @startLSN_str as PkgLSNEnd

This then returns data to a string that I can put in a package String variable.

They dont make this easy 🙂