You can insert data separated by commas without splitting the IDs but I wouldn't suggest that you do that. If you didn't split on the insert, you'd always have to split on the select. Plus, you're just asking for nothing but problems in the long run. Not only that, it violates the First Normal Form of database normalization:
"All attributes must be atomic, that is, only one single value represented in a single attribute in a single instance of an entity."
- SQL Server 2000 Database Design, WROX Press, pg. 148
If it was me, I wouldn't go there.