How do I connect to an in-memory, shared cache database?

I'm trying out the in-memory shared cache feature of SQLite 3.7.13, via the ADO.NET provider. The following connect string works, but yields a non-shared-cache db:

Data Source=:memory:

When I try any of these:

Data Source=:memory:?cache=shared
Data Source=file::memory:?cache=shared
Data Source=file:x?mode=memory&cache=shared

I get the following ArgumentException when opening a connection:

Invalid ConnectionString format for parameter "Data Source"

What should the connect string look like for SQLite in-memory shared-cache databases?