This is not exactly what you want but it is a close approximation of it. It will take a random word from 5 letter word list and 6 letter word list and output all possible 4 digit combinations in between the words and print it to a file, ready for further use.
You can repeat this as many times as you like and save all these files as dictionaries or even merge them if you wish to do so. Also this will save your computer from choking itself to death, both space and performance wise.
A python script:
import sys
orig_stdout = sys.stdout
f = file('pass_list', 'w') # Specify the name and path of the output file.
sys.stdout = f
import itertools
from itertools import product
import random
digits = '0123456789' # Set the digits.
prefix = open('5-letter.txt').read().split() # Specifiy the path to 5 letter word list.
first = random.choice(prefix)
suffix = open('6-letter.txt').read().split() # Specifiy the path to 6 letter word list.
last = random.choice(suffix)
for keygen in itertools.product(digits, repeat=4): # Specify the length of the digit combinations.
print (first+ ''.join(keygen)+last)
sys.stdout = orig_stdout
f.close()
Note: Both of the input .txt files need to have one word per line in order to work this properly.
EDIT: I would like to add that you may print out a bigger file if you want but know that chances are, although very slim, that prefix and suffix words will be repeated in the output file. Here is how you can modify the code.
prefix = open('5-letter.txt').read().split()
a = random.choice(prefix)
b = random.choice(prefix)
c = random.choice(prefix)
suffix = open('6-letter.txt').read().split()
x = random.choice(suffix)
y = random.choice(suffix)
z = random.choice(suffix)
for keygen in itertools.product(digits, repeat=4):
print (a+ '' .join(keygen)+x)
for keygen in itertools.product(digits, repeat=4):
print (b+ '' .join(keygen)+y)
for keygen in itertools.product(digits, repeat=4):
print (c+ '' .join(keygen)+z)
Not very pretty but it gets the job done. However, as stated above, chances of duplicate increase with repetition. And the bigger the file, the more annoying is to manually edit it.