One tsp of nutrient per gallon (probably about 200ppm of YAN) should be more than enough to ensure complete fermentation, especially with EC1118. What is the SG of the stopped cider? If you aren't able to measure it, "taste" should give you a rough idea. With EC1118 and nutrient, a fully fermented cider should be very dry and tart. i.e. no sugar left, hence no bubbles.
I have done a new yeast starter with nutrient in the past to kick things along, but now I don't think that extra yeast is necessary unless you have killed all the EC1118 which is quite unlikely given that it bubbled for up to 10 days. Even residual sulphite should have dissipated after a couple of days. The key to what is going on is to measure the current SG since as you suggest, adding extra juice (i.e. sugar) should have started it up again. Nevertheless, you might try adding a new starter if all else fails.
The extra litre of juice would have about 130g of "sugar" (really 110g of sugar plus other density components, but near enough for what we are talking about). So, when added to the gallon of "fully fermented" cider it should have resulted in SG 1.010 or around 27 g/L of sugar which would have been enough to continue fermenting.
So, if the current SG is substantially below 1.010 the fermentation has continued. If well above 1.010 then your original cider hasn't fully fermented. This might give you an idea of what is going on.
Cheers!
Whoops, edited the original post to change SG 1.008 to SG 1.010 because I forgot a US Gallon is just under four litres whereas I calculated on my "gallon" carboy which is 5 litres. It didn't make a big difference but might as well get it right... Sorry!
