Using "et al." in maths papers
While mathematics is not my area of specialization, I think that in your question you are making a general and IMHO wrong assumption about the importance of the name, appearing in the "et al." construction. Essentially, this construction is used only for the purposes of convenience (brevity for readability) and not for implying the amount or importance of work, performed by any of authors.

When people see the "et al." citation, I am pretty sure that decent scientists immediately refer to the full citation in a reference list in order to obtain full information on all authors of a paper in question. Therefore, I believe that the "problem" that you have described in your question is really an artificial one, which exists only in your imagination (due to the incorrect assumption, mentioned above).