Translate query using APPLY to run under compatibility level 80
The results from that query will not be scoped to particular database. They will show activity across the whole instance.

In general, it would be quite difficult to provide information at this granularity, because queries can access data from more than one database (Azure SQL Database aside).

In non-trivial queries, accounting for costs on a per-database basis (e.g. after joins and aggregations have been performed) would be pretty much impossible. Some DMVs do provide information about the context database at the time a query was executed, but again, the query might have accessed objects in an entirely different database(s).

The easiest answer, therefore, is to simply run the query in the context of a database that is set to compatibility level 90 or higher, such as tempdb or master. It will not affect the results (aside from not producing an error).

If this is not a suitable solution, please edit your question to clarify.