I notice Stevie Wonder and Cory Henry have their Harpejjis off angle instead of front and center, in their stage setups.
Marcodi claims you can pluck, strum, and slap on a Harpejji. Slapping like on bass seems the most doable - just fret with your fretting hand and slap with appropriate part of your palm/thumb like on bass. That’s how it works on Stick. Strumming and plucking look less ergonomic on Harpejji.
For quick repeated notes, you could probably just hammer-on a fret with one finger, then hammer on the same pitch but different fret with another finger. On guitar, a similar approach is fretting the same pitch on the G and B strings, picking the G string with a pick and picking the B string with a free finger. The same could be done on other pairs of strings, but the reach is shortest on G&B.
Generally though, I think the Harpejji would benefit more from a Clavinet style of playing than guitar/bass styles if you want to get funky on one.
Here’s a guy playing one of the most iconic funky Clavinet parts ever at 1:24