[plt-scheme] persistent data (i.e., between runs)

I feel as though I should know the answer to this question, but I don't:

Is there any simple way to preserve a value between evaluations of a  
program in the definitions window?

The situation is this: I'm working with a big xml expression (35 Meg  
in s-expression form, 7 Meg written as a .zo), and successive  
evaluations of the program that reads the data from disk are  
squonching my DrScheme.  In particular, DrS gets many megabytes  
bigger each time I evaluate the program, and running it more than  
four or five times crushes my poor little 512Meg Mac Mini.  More  
precisely: I have to force-quit DrScheme.

Now, this may or may not be a memory bug--DrScheme 3m lasts much  
longer, but still grows by ten or twelve megabytes each time I hit  
execute--but I'm thinking that there should be some way to keep a  
value around and not have to keep reading it from disk.

My first thought was that by pushing its evaluation into a module  
that was require-for-syntax'ed that I would avoid the re-evaluation,  
but some small experiments showed me the fallacy of this.

My second thought was that I could write a tool that attached a  
module containing the definition to the namespace before evaluating  
the definitions window, but this seemed complex and (hopefully)  
unneccessary.

Is there an easy way to get what I want?  A help desk search on  
'persistent' turned up nothing.

Thanks,

John