I hope you don't mean dynamic equation generation and fitting. This you are not going to do.

In system programming is something you can do and I have done.

Xilinx application note XAPP058 describes exactly how to program an XC9500 family CPLD using an 8051. This can be done on-the-fly, on the condition that the CPLD is not needed for basic CPU functionality (the CPLD is unavailable while it's being erased and reprogrammed).

The Xilinx example code works but it is horrible (unnecessary use of signed and big variables, slow math, etc.). I cleaned up the code and got about a 4X improvement in code size and speed.