AM3505 sys_clk run at non integer decrement

We want to run sys_clk on the AM3505 at 12MHz rather than at 13MHz due to some truncation issues. Much of the documentation suggests we can run sys_clk at 12MHz.  But other places in the documentation state that the input clock can only be 26MHz and the only way to modify sys_clk is to divide it by 2.  Can we run the sys_clk at 12Mhz and if so, how can it be done?