I use a Gossen Luna Pro F (for no special reason other than that's the meter I happen to own).
To use the meter for pinhole, I set the film/paper's ISO on the meter, then reference the exposure time (in seconds) for f/128 on the Gossen (the meter's highest f-number) then do the conversion this way:
(camera's f-number / 128) ^2 * exposure time for f/128 = camera's exposure time.
This does not take into account reciprocity failure. But I mostly shoot paper negatives, which have virtually no reciprocity issues at most normal exposure times for pinhole (upwards of ten minutes I've seen no significant reciprocity failure for paper).
I end up doing the calculation for the camera's f-number / 128^2 part of the formula ahead of time and afix this number, as a constant "K", to the camera with a label maker. Each of my pinhole cameras have their "K" factor number labelled thusly. In the field I do the metering on the Gossen, reference the exposure time in seconds opposite f/128, and multiply that number by the camera's K-value to yield the working exposure time. Very easy and also very accurate.
~Joe