load and use a ".o" file?

[lifetime n00b <anonymous@yahoo.com>]

I've been trying to educate myself on how to do this, but I can't seem 
to find the answers I need. In concept, what I need to be able to do 
seems like it should be simple, and so I'll give a simple example.

There is a main program loop already running, and there is a ".o" 
compiled object file (compiled with gnat) which *hasn't* been linked 
into the main program, but it has a procedure or function in it I want 
to call. Let's say it is very simple function which was compiled from this:

function HiThere return String is
begin
	return "Hi there!";
end HiThere;

Instead of linking this into an executable, it is just compiled with 
say, "gnatmake -c hithere", to get the "hithere.o" file we're interested in.

Now, how can I load this "hithere.o" file into an already running 
program (without linking it in beforehand) and then call the "HiThere" 
function from that program (which was also written in Ada)? Would the 
information in the corresponding .ali file be of use? Maybe I'm thinking 
about it wrong, and the source which compiles to the object file needs 
to have some access types or some other mechanisms in place? Note that 
I'm not talking about using a .dll or .so file, just the .o file.

Any guidance would be appreciated.