character name question

Hi all,

I have a lot of code in MCL that I want to port to Allegro CL. So I'm  
creating an MCL compatibility file that will make MCL specific code  
to work on Allegro CL unchanged as much as possible (only a small  
subset of MCL, not the whole thing). So here is my question:

In MCL, they have additional character names: #\UpArrow, #\DownArrow,  
#\ForwardArrow, #\BackArrow, etc. Is there an easy way to add  
additional character names in Allegro CL? I've tried setting my own  
sharp-backslash macro reader, but I have problem calling the original  
sharp-backslash macro reader. Do I need to muck around with the  
readtable? My experience doing this kinds of thing is quite limited.  
Any pointers will be appreciated. Thanks.

--ronald