Coupon Query

[BellesBows]

I was wondering if there was a way to implement the following.

I want my coupons to work in conjunction with each other but only in certain circumstances.

For example:

I have a cart rule setup so that a customer can buy and 3 of a particular category and receive a £1 discount i.e 3 bows for £5 when usually £2 each

I also want to be able to offer all new customers 10% off their first order but exclude items that have already received a discount so the 10% wouldnt apply to the above but would apply to any other items in the cart.

At the moment it works like this

Customer buys 3 bows £2 each and receives a discount making it £5

They also buy another bow at £3.99 making the sale £8.99

The current 10% would take 10% off the whole order but I only want it to take it off the £3.99

I have tried customing the conditions of the coupon to exclude items already discounted but this only works on "price drop" items.

Any ideas?