Removing configure flags?

[HiPhish]

Hello everyone,

There is this shell scripting test framework called Roundup which I would like 
to package for Guix:
https://github.com/bmizerany/roundup
http://bmizerany.github.io/roundup/

It looks like the author has written his own configure script rather than 
using autotools to generate it, and it chokes on the default configure flags 
provided by Guix:
https://github.com/bmizerany/roundup/blob/master/configure

The culprits are the `--enable-fast-install` flag and the `--build` option. 
There is no need for either of those since it's all just shell scripts anyway, 
so is there a way to remove them? I know I can add flags, but I haven't found 
anything in the manual about removing some of the default flags.