floating point operating in vhdl (fixed_pkg)

This thread is the closest I've found to addressing my issue, so I hope you don't mind me reviving it. I am using fixed_pkg in my VHDL design to do fixed point arithmetic. I compiled it into my Quartus work library so didn't create the ieee_proposed library:

library IEEE;

use IEEE.std_logic_1164.all;

use IEEE.numeric_std.all;

use work.fixed_pkg.all;

My design compiles and synthesizes successfully in Quartus 16.1.1 Standard, but not in ModelSim 10.5a:

Error: (vcom-11) Could not find work.fixed_pkg.

Now I've read that I can change the location of fixed_pkg from "work" to "ieee" since ModelSim supports it. However, the compilation of my project is heavily scripted, so I need to use the same source files for both the Quartus and ModelSim synthesis. How can I do this?