Hi guys, looking to bulk on lean muscle but limit fat gains as I go...

I've been working out on a weights split for about a month and a half now, doing....

day 1- back/biceps
day 2- chest/triceps
day 3- legs
day 4- shoulders
day 5- REST DAY

about 25-30 sets on each workout, proper blasting that body region.

... and I'm definately bulking on muscle, seeing my lift weights increase loads and it's plain to see I'm getting bigger. However I'm still wary of putting on fat (beyond what's unavoidable), and I want to retain the basis of CV fitness. So I'm keen to try what I've been reading about everywhere- high intensity interval training. Tried it a coupla times- 1 minute at 12 kph treadmill followed by 30secs at 19kph sprint, for 20 minutes. Dripping with sweat by the end of it, and feel like it's stripping the fat off me for the rest of the day, so I feel it's doing me good, and will be functionally useful for the footy etc and taekwondo I occasionally do :P

The question is though, from the ideal of wanting to bulk on lean muscle, WHEN should I be doing these HIIT sessions? As i see it, I have 2 options:

1) HIIT on 'rest days'. This would be the easiest to incorporate around work etc, but I fear that I wouldn't be giving my body enough time to rest for muscle growth. But having said that, I'm only working each body part with weights 1-2 times per week, so would be resting each muscle group passively most of the week... so maybe a 20minute HIIT session on a rest day from weights is fine and wont hinder muscle growth? This is what I'm leaning towards doing, and chucking in the odd total rest day every now and again, when the body tells me i need to.
i.e.
day 1- back/biceps (weights day)
day 2- chest/triceps (weights day)
day 3- legs (weights day)
day 4- shoulders (weights day)
day 5- 20 minutes of HIIT cardio, and rest of day resting

2) Somehow incorporate HIIT into 1 or 2 days that I'm also doing a weights session. i.e. HIIT in morning, weights in evening or vice versa. This would be hard to do, as I guess I'd have to separate the HIIT session from the weights session to avoid catabolism issues and enable me to re-energise for the weights, BUT I'd still be able to have a day or so of total rest per week. BUT this would also be hard to do when I'm working, as time-wise, 2 separate gym sessions are a bit hard to fit in.

Any help as to which would be most recommended to help me keep the fat off but still let me pack on lean muscle would be HUGELY appreciated!

Thanks, Paul

Personally, I'd do the HIIT on the rest days, the reasons being that from a CV point of view I'd imagine it very tax-ing on the body to do a full weight training session followed by HIIT, and I'd say if you are able to do it you're probably not doing, HIIT more Medium-Light IIT(MLIIT if you will)

From a bulking point of view, once you eat to a calorie surplus, with these cardio bouts included(calorific needs + calories used + suprplus), you should still bulk.