Allergic has good advice!
I wanted to attempt 'dual fuelling' and it didn't work at all for me. i.e. I just didn't bother picking up the ecig at all, and stayed fully on the fags. I kept thinking: 'next time I want one, I'll use the ecig instead', but I kept picking up my cigs instead.
Once I'd decided to make the switch (which was months, if not a year later), I realised that- for me- it had to be a clean break. But to make it easier, I used a nicotine patch on top of vaping for the first 4-5 days. I can't say whether or not it's completely safe to do this, as obviously I was getting a LOT of nicotine those first few days (and I was wired!). But it was the only way I could do it.
And even then, it was still a bit hard- because I was breaking all the habits and rituals around rolling my own fags and standing outside etc.
But it was much, much, much easier than any of my previous attempts to stop smoking.
Obviously, this might not seem relevant to you, because you already ARE dual fuelling. But I just thought I'd mention using a nicotine patch alongside the vaping, in case you think it could help you. (But with a BIG disclaimer to think carefully about it because nicotine poisoning is always a possibility! Although as I understand it, it would be usual to feel sick/dizzy/get a headache before anything more serious happened).