How to find workaround for xml.value() function in babelfish?

We encountered an xml issue during the poc of babelfish migration, how to rewrite a user define function based on 64-bit encryption that is very common in sql server. The following code you can find on many web site

CREATE FUNCTION [dbo].[FnBase64Encode](@src varchar(max))
　　RETURNS VARCHAR(max)
as
begin
　　declare @bin varbinary(max)
　　set @bin=Convert(varbinary(max), @src)
　　return cast(N'' as xml).value('xs:base64Binary(xs:hexBinary(sql:variable("@bin")))', 'varchar(max)')
end
GO

We know that the current version of babelfish(1.2.1) does not support xml methods such as xml.node and xml.value, is there any solution or sample code for this case?