I would advocate for arguing for no (de facto, even if not de jure) corequisites for such a course. We don't have any, nor prerequisites, and I think that is the case for a number of institutions in Massachusetts.
This course often is a challenge for some pre-service teachers, to be sure. But I can't think of any course that would bear college credit that would resolve that issue - honestly, not even some of those that cannot bear college credit would do so for the type of content usual in these courses. Properly done, this course often starts to fill in what no prerequisite course can - that is to say, a sense of understanding why mathematics is not just a set of arbitrary rules to memorize. You do need a high-quality and compassionate instructor for this - we have been very fortunate to have someone in that role for many years.
What might sweeten the pot for your administrators is if you were to have a "lab component" or "tutorial" for students who would not meet whatever prerequisite had formerly been in place. (As SvH points out in the comments, this can be formally labeled as a corequisite.) Especially for ones who still have trouble with times tables or kinds of triangles or percents (and I wouldn't be surprised if you had some), that might be a mechanism that satisfies all constituencies while preserving your pedagogical insight that a corequisite as such would be a hindrance.