If you are comfortable with that, I think it might work. The only way to know is to try it when you can safely monitor, keep an eye on his numbers in the first few hours and then in that +5 range. Even if it's too little insulin, I am thinking it is better to have some in his system so you aren't looking at the 500s again tonight. (see my caution about his inappetite problems below)
Do you know how to steer a lower number with food? If he is in the 70s or so early on, feed a little more extra regular food. If he drops below 50, feed some gravy off high carb food (always should be in your hypo kit) and retest in 15-20 minutes to make sure he is rising, not falling. If he is still falling, rub some honey on his gums and do the test again in 15 mintues. Note these are ReliOn type numbers. If you are using the AlphaTrak, add approximately 30 to each number. If he is not still not eating, this makes the process more complicated and might be a reason to up that number above 250.
But ALWAYS go with your gut. If you don't feel some advice is wise, then disregard it. You hold the needle, you love the cat, you decide.