I'd look at the watts carefully.

Hub dynamos are available in 1.5W, 2.4W, and 3W.
The old Bottle dynamos are up to 6W (unregulated?)

Headlights are also made for different watts.

So, for example, the B&M One-Five is designed for 1.5W. So, you should be able to wire two of them in parallel (or serial) to get 3W (see below).

However, that B&M One-Five is rated at 30 Lux.

The B&M IQ-X is rated at 100 Lux.

To hack stuff together, you'll really need detail specs of Volts, Amps, Watts

Watts = Volts * Amps

I think it is:
Parallel wiring: Volts constant, Amps half
Serial wiring: Amps constant, Volts half.

A battery sink will help with evening out the power input/output.

The notes indicate that the B&M One-Five could be damaged by a 3W dynamo. I'm a bit surprised by that, but to some extent it will depend on the volts.

So, for example, a 12V, 1.5W (0.125A) light should be perfectly happy being connected to a 1000A, 12V car battery, but it could be damaged by a 24V input, even at low amps.