Sounds like purgatory. Soft grassy tracks with 35mm tyres, ooft.
Your 2 options, that I can think of anyway, are up nan bield and then west onto high street, or up garburn and turn off north at the top onto yoke/illbell/mardale Ill bell/thornthwaite and onto high street.
The latter would probably be the best option tbh. There will be quite a bit of pushing, both up and down though. The tops of the hills up there have some rocky descents heading north, but could be avoided to an extent as frostwick and mardale both have wee grassy singletrack routes contouring round them as well as the routes over the top.