Bill Kapaun 's idea is what I first thought - add something with some weight a bit further forward. A basket, a pair of water bottles, I don''t know what else. The further forward you mount the weight the more effect it will have, but likely too far forward will make whatever it is inaccessible from the driver's seat.
Another option is to lower the tire pressure in the front wheel. Since it has so little weight on it you can run it pretty low without fear of pinch flats. A tire at lower pressure will better follow the bumps in irregularities in the road and increase traction.
And while on the subject of tires, putting wider tires on the rear and a skinnier tire on the front (or simply more pressure in the R and less pressure in the F) will tilt the whole rig forward a bit, which will put marginally more weight on the front. Tires for 26" wheels are commonly available in widths from 1" up to 3+". 1.25 on the front and 2.5 on the rear will make a noticeable difference. You'll still want to run the front tire at pretty low pressure for maximum traction.
Being limited by the steepness of the road or trail is a common situation in mountain biking, and this leads to my final suggestion - practice applying the power in the smoothest possible circles to avoid any surges that will break the tire loose. I don't know you or how smooth you are so this may or may not be helpful advice.
Best of luck!