Use the face of the DI. Assume you're at 180/20 and want to go to 090/30.
Pick biggest distance (30), take radius of DI as 30 and the Navaid as the centre. Find current position as 2/3 of the DI radius in 180 direction (radius represents 30) and desired point as 090 on the circumference (radius represents 30), hold pen or other straight edge over the 2 points then move pen up to pass over the centre - wherever it's touching on the circumference is the magnetic track between the 2 points.
Turn on to track, use MaxDft to assess drift and then turn on to heading.
Sounds complex, it's actually very easy!
HFD