Trimming A Trailing Comma

I have the following query:

SELECT DISTINCT
	Table4.Name,
	(SELECT DISTINCT
		ltrim(rtrim(Table2.PCost_Center)) + ','
	FROM 
		Table2 
	where 
		Table1.Company_Code = Table2.Company_Code
		and Table1.Job_Number = Table2.Job_Number
		AND Table2.PCost_Center <> ''
	FOR XML PATH('')) AS Cost_Centers,
	(SELECT  DISTINCT
		ltrim(rtrim(Table2.PCode)) + ','
	FROM 
		Table2 
	where 
		Table1.Company_Code = Table2.Company_Code
		and Table1.Job_Number = Table2.Job_Number
		AND Table2.PCode <> ''
		FOR XML PATH('')) AS PCodes,
	Table1.Job_Description,
	Table1.Job_Number,
	Table3.Alpha_Field AS Site_ID
FROM 
	Table1
	LEFT OUTER JOIN Table2
		ON Table1.Company_Code = Table2.Company_Code 
		AND Table1.Job_Number = Table2.Job_Number
	LEFT OUTER JOIN Table3
		ON Table1.Company_Code = Table3.Company_Code 
		AND Table1.Job_Number = Table3.Job_Number
		AND Table3.User_Def_Sequence = '000003'
	LEFT OUTER JOIN Table4
		ON Table1.Company_Code = Table4.Company_Code 
		AND Table1.Customer_Code = Table4.Customer_Code 
WHERE 
	(NOT (Table1.Customer_Code IS NULL OR Table1.Customer_Code = '')) 
	and (Table4.Company_Code = 'ENG' or Table4.Company_Code = 'INC')

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The sub queries which produces Cost_Centers and PCodes produces a value that always ends with a comma (unless the result is null).  How can I trim off the trailing comma?