Param spec for gvalue

[Kent Schumacher <kent structural-wood com>]

How do I write a param spec for a GValue?  I see
I've got param specs for chars, uchars, boolean, int,
uint, long, flags, etc..., but I do not see any
g_param_spec_value (or g_param_spec_gvalue).

Basically I want to add a read/write property to a
cell-renderer that takes a GValue.

Thanks,
Kent