[ODE] Is it possible to make a body non-movable?

[michael kapelko]

Is there any function, or is it possible only with a joint?
I'm making a little editor, and I need two types of objects: which are 
pulled by "gravity gun" and which push a player towards itself when 
using "gravity gun" (anti-gravity gun effect?). So I wonder how to make 
certain bodies non-movable.
I think now only of a fixed joint between ... hm... but the map is just 
a geom, I can't create a joint between map and object, i.e., between 
geom and body. A body must be created for an object in order to interact 
with a "gravity gun". And the map certainly needs no body, only geom.
Any ideas?
Thanks.