Special data:
(1,1): The number so far (starts at 0).
(2,2): The negative of the bit to be set (starts at -1).

(2,2) is doubled each time, and tested for zero.  This is an overflow trick that
only works on binary computers, and if Wierd is ever ported to ternary
computers, this program will run indefinitely or at least much longer than it
should.

In detail:
1.  Put 0 in (1,1).
2.  Put -1 in (2,2).
3.  Get (2,2).
4.  Push zero (dance "left left right") and subtract.  This is necessary because
    a condition can only follow a 45 or 315 turn (there needs to be space for
    turning back).  Following a 45 turn is quite useless though...
5.  Test.  If zero, go to step 17.  Otherwise, continue to step 6.
6.  Use a 45/315 split to randomly chose whether or not the bit is to be
    included in the number.  Depending on the result, either continue to step 7
    or jump to step 11.
7.  Get (1,1).
8.  Get (2,2).
9.  Subtract (see why (2,2) is negated now?).
10. Put the result back in (1,1).
11. Get (2,2).
12. Push a zero through the "left left right" dance.
13. Get (2,2) again.
14. Subtract twice.
15. Put the result in (2,2).
16. Go back to step 3.
17. Get (3,3) and put in (2,2) (for output subroutine).
18. Output as a binary number, using output.w.
19. Done!

Since the output routine is O(n), you should modify the interpreter to use a
smaller data type (short or even char) if you want the program to terminate this
year.  Of course, since outputted number is random, you just might be lucky and
get a very small number which can be printed in less than a second.  The random
number generation itself is quite fast.