SQL Server 2008 :: Redirect Insert Data Into Another Column

I was wondering if there was a way to redirect an insert to another column...

Example:
Original Insert Statement:
INSERT INTO [table] ([columnA], [columnB])
SELECT '2015-01-01 00:00:00', 99.99

We have changed [columnB] from a decimal(19,9) to a computed column. So instead, we added another column [ColumnC] to take [ColumnB]'s insert data. I thought we could've used a trigger instead of insert, but that fails with the message "cannot be modified because it is either a computed column or is the result of a UNION operator".

This is the trigger I was using:
CREATE TRIGGER [Trigger] ON [table]
INSTEAD OF INSERT
AS
INSERT INTO [table] ([columnA], [columnC])
SELECT [dataA], [dataB]
FROM Inserted