Use entities instead. In the conf/ directory, create a file named entities.local.conf. Add these lines:
(sp)  
(SP)  
When you want a space character, use (sp)
in your document for a standard space and (SP)
for a wider space. These derive from when fonts were lead type, and the wide space was created as the width of a capital M and the narrow as half M and were named en and em.