Custom Functions

Would it be possible to allow custom functions? You'd set a name and a list of arguments, then allow the user to type in some javascript or php or something to determine what's shown in the cell or returned to the cell, like this:

Name:
[_cube________]

Arguments:
[_number______]

Code:
[ return $number * $number * $number; ]
[__________________________________]

to be used as

=cube(4)
or
=cube(A9)

-or-

Name:
[_dice________]

Arguments:

Code:
[ $b = rand(1,6); ]
[ return $b; ]
[______________]

to be used as

=dice()