You’ll able to get some climbs in somewhere presumably, but the biggest problem will be adapting to the terrain. Fell terrain is vastly different to road, in that it is totally unpredictable and uneven. You can’t settle into a rhythm like you can on the road, and it will soon sap even the fittest road runner if they’re not used to it. I’ve had the same problem living in the flat suburbs of Manchester. Things I’ve thought of are:

Running ladders (as used in football). They’ll help foot speed.

Running in and out of tyres (as in the army).

Step machines

Slalom style, quick, in and out of cones type running.

Doing endless laps of boggy football pitches.

Hope this helps.