Bottom line, you can't put a * into a float column, it's not a float. It you want to badly mess thing up, you could convert the column to a varchar then spend huge time and effort fixing bad data, correcting 'broken' calculations and making massive amounts of work for yourself. If the data is numeric then the column should not be a varchar.
You can convert nulls to * in the queries that retrieve from the table.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability