As Ember Spirit, is there a trick to reliably casting Chains during a single-target Sleight?

Casting Searing Chains while in Sleight of Fist's animation is a really useful technique to almost instantly chain enemies from a safe distance. Here's Miracle- demonstrating on Slark, at 6:18:

I can do it when Sleight hits 2+ targets, just by flicking WQ. I get it every time, because the animation is long enough.

However, when Sleight hits only 1 target like in that video, Sleight's animation is crazy fast, and I'm finding it really difficult to consistently trigger Chains during it. Even if I bring my middle- and ring-fingers down at almost the same time to QW, I still usually whiff it!

I've already tried Shift-queueing Chains after Slight, but that totally fails, because Chains only triggers once Sleight ends.

Something tells me there's a trick to this, because I see skilled players hit it so consistently. If the trick is "play Ember constantly for 6 to 8 weeks", that's OK too. But before I start on that, is there something I'm missing?

Solution 1:

Use the Demo feature to practice mechanical skills like the sleight+chain combo.

Although I am not a pro(not even close) and have only played around 40 Ember Spirit games I can land most of my combos properly. I spent around half an hour continuously practicing that combo on a single hero with various levels of sleight. After that I spammed Ember in a few casual games. Trust me this works like a charm.

In order to open Demo, click on the HEROES tab then select Ember Spirit. Right next to his skills you can see a box which says DEMO HERO. Click on that and you'll be able to figure out the rest.
It basically creates a small area where u can practice last hitting and check out different abilities of any hero. You can also spawn dummy and AI enemies.

Solution 2:

The timing is very reliable when you get it down, you need to get used to the amount of time it takes from clicking w until the skill is actually cast, but once you get it a few times it becomes second nature.

As an aside/extra, you can do more than just chains during sleight of fist! ember's location is fully set right next to the enemy and you aren't stopped from acting in any way, one of my favorite combos to do (very difficult but very fun) is to also leave a remanent on top of the person you use chains on, since you can cast it while you're right next to them, you can also use this as a way to escape slows, if you sleight a creep camp and cast a remenant while you're 'over there' you can get much better milage and can easily escape otherwise guaranteed deaths.