I'm in C minor and want to modulate to its subdominant key of F minor. One way to do this is to introduce the tonic flat seventh chord C-E-G-B♭, which is the dominant seventh chord of F minor. Other than outright juxtaposing this chord next to the tonic triad of C minor, what are some clever ways of 'smuggling' B♭ into my chord progression? Something with the descending minor scale perhaps?
Here are some simple ideas for getting from C minor to F minor without anything too outlandish. Obviously these are schematic. Since the dominant seventh chord is about as unsurprising as it gets, if you want to 'smuggle' the modulation in you have to go somewhere else first. The first example is about as simple as it gets without introducing the dominant seventh directly. The second feels more like it's going to F major, so F minor can be a slight surprise.
One possibility is to go the stereotypical Bach route: prepare a normal cadence in the tonic C minor, but instead of cadencing on C minor, cadence onto a C7 chord.
The following example is in C major, but you still get the idea. Hear it here.
You don't need to smuggle B♭, it's in C minor already. The note that needs to be introduced is E natural.
If you want something a bit less obvious, try Cm, B♭, B♭m, C7♭9, Fm.