[metapost] How to instruct mpost to use ConTeXt?

[Nicola]

Hi,
as far as I understand, this:

verbatimtex %&latex

and this:

mpost -tex=latex ...

are equivalent ways (and none of them mandatory) to tell mpost to use 
latex to typeset the labels. For ConTeXt, I've found that 'verbatimtex 
%&cont-en' works. What is the equivalent from the command line? I've 
tried

mpost -tex=texexec ...

and even

mpost -tex=context ...

but both fail with 'DVI generation failed'.

Nicola