You can perform bulk operations on multiple documents without an index by using the `USE KEYS` operator with a list of document IDs. This allows you to query specific documents based on their keys, even if there is no primary or secondary index created. The `USE KEYS` operator enables you to narrow down your query results to only those documents that match the specified keys, providing fast performance similar to how it would be achieved with indexes. By utilizing this operator, you can write N1QL queries on Couchbase Buckets without relying on indexes, making it possible to perform efficient key-based operations.