As a follow up, I've found a way to get values out of a stored proc without using bind_param_inout -

$sth = $dbh->prepare('
        declare @DDI UDTDDI, ... @AvailableInd UDTFlag
        execute p_ccs_MakeBooking @ClientAccount="xxxxxx", ... @DDI=@DDI OUTPUT, 
        @CPIN=@CPIN OUTPUT, ... @AvailableInd=@AvailableInd OUTPUT
        select @DDI as DDI, @CPIN as CPIN, ... @AvailableInd as AVIND');

Using this query I can just read my outputs using regular fetch statements.

Thanks