Use expression to set the connection string for your excel connection. Use a variable to set the conection string. You can do this by Properties->Expressions->ExcelFilePath-> Set your vairble here.
Now use Execute SQL Task to set the value of this variable. In the Execute SQL Task Editor, set the ResultSet as SingleRow, now click on Result Set on the side menu and click Add to add a vairble mapping. If you are uisng OLEDB conneciton use 0 as Resultset name and select your variable.
This should set the variable to a value from your table and will set the Excel File Path for excel to this value.