Хмм, что-то похожее на правду:
protected override StatementSyntax CreateUsingStatement(LocalDeclarationStatementSyntax declarationStatement, SyntaxTriviaList sameLineTrivia, SyntaxList<StatementSyntax> statementsToSurround)
{
var usingStatement = SyntaxFactory.UsingStatement(
declaration: declarationStatement.Declaration.WithoutTrivia(),
expression: null, // Declaration already has equals token and expression
statement: SyntaxFactory.Block(statementsToSurround));
return usingStatement
.WithCloseParenToken(usingStatement.CloseParenToken
.WithTrailingTrivia(sameLineTrivia));
}