Edit connection manager connection string at runtime with c#

This is the first time I have used SSIS, so please bear with the ignorance.

I have a super simple package that inserts x000's of rows into a temporary table. The data source is a file that the user will upload. I need to be able to tell the package what file to upload. I'm thinking the simplest thing would be to edit the connectionString property of the SourceConnectionFlatFile at runtime. Is this possible? What form should the file path be in (UNC, other)? And, are there any other considerations I should be aware of?

Thanks!

Package configurations were designed for just this purpose.