Concatenate String And Pass To FORMSOF?

The following query works perfectly (returning all words on a list called
"Dolch" that do not contain a form of "doing"):

SELECT 'Dolch' AS[List Name], dbo.Dolch.vchWord
FROM dbo.Dolch LEFT OUTER JOIN
dbo.CombinedLexicons ON CONTAINS(dbo.Dolch.vchWord,
'FORMSOF(INFLECTIONAL, "doing")')
WHERE (dbo.CombinedLexicons.vchWord IS NULL)

However, what I really want to do requires me to piece two strings together,
resulting in a word like "doing". Any time I try to concatinate strings to
get this parameter, I get an error.

For example:

SELECT 'Dolch' AS[List Name], dbo.Dolch.vchWord
FROM dbo.Dolch LEFT OUTER JOIN
dbo.CombinedLexicons ON CONTAINS(dbo.Dolch.vchWord,
'FORMSOF(INFLECTIONAL, "do' + 'ing")')
WHERE (dbo.CombinedLexicons.vchWord IS NULL)

I have also tried using & (as in "do' & 'ing") and various forms of single
and double quotes. Does anyone know a combination that will work?

FYI, in case this query looks goofy because of the unused "CombinedLexicons"
table, it is because the end result should be a working form of the
following...
Figuring out the string concatination is just a step toward this goal:

SELECT 'Dolch' AS[List Name], dbo.Dolch.vchWord
FROM dbo.Dolch LEFT OUTER JOIN
dbo.CombinedLexicons ON CONTAINS(dbo.Dolch.vchWord,
'FORMSOF(INFLECTIONAL, ' + dbo.CombinedLexicons.vchWord + ')')
WHERE (dbo.CombinedLexicons.vchWord IS NULL)

Thanks!