If you're not averse to doing a little math, you might be able to fudge it with the gauge you're at now.
Calculate the quotient of your gauge divided by the pattern's gauge:
Then multiply every number of sts given in the pattern by that number, rounding up when you get a remainder (since the pattern's written for medium/large and your husband's a large).
Tada, you have a converted pattern. Vertical gauge isn't as important as horizontal gauge, just knit for however many inches the pattern tells you in each part and it should work out. (Or, you could do another proportion of your vertical gauge/pattern's vertical gauge and calculate what you should multiply the rows by in the same way you figured out the horizontal gauge.)
Here's an example. Say my gauge is 10sts/inch and the suggested gauge is 5sts/inch. 10/5 = 2, so I should multiply the number of sts in the pattern by 2. It tells me to cast-on 50 sts? I cast-on 100 sts. I have to decrease 2sts at the beginning and end of every row every inch or so? I decrease 4sts at the beginning and end, yadda yadda yadda. It's a rough conversion, but it should still give you a good approximation of the original pattern.