Try this:

Create a stimlist with the 5 words and call it something like mylist.txt.

On the first trial, randomly draw one from the list, using $mylist. Then add 4 trials that repeat that stimulus, using the syntax like ?b1t1s1 (see link below for repeating a particular stimulus on a subsequent trial)

On the sixth trial, randomly draw another word from the list using $mylist. This time add just 2 trials that repeat that stimulus, using the syntax like ?b1t6s1.

Finally, add 3 more trials--each randomly drawing from the stimlist, using $mylist. These will each be presented just once.

Finally, assign all the trials a WGR value of 1 to randomize their order.

Take a look at the section on "using previous stim" in the users guide:

www.empirisoft.com/directrt/help/directrt_samples_of10_using_previous_stim.htm

Let me know if you have any trouble with it.