You could use an add-on neutral lug strip. These are sold at home
centers in the vicinity of the service panels, and are used to add more
neutral lugs to existing panels.

The strip has about 10 new spaces for neutral wires, each with a
screw-down lug, exactly like you'd find in a service panel. As I
recall, these were about three bucks the last time I bought a set.

James Owens wrote:
Can I do this with one wiring cap? Or could I solder them together?