Your friends are the Blink Dagger + Shift Key and Tabs

My fingers to slow to pull it off but essentially you need to

1. Main Meepo got blink dagger
2. Find victim, throw net, channel Poof and shift blink dagger to victim position
3. At same time tab to 2nd Meepo and Poof and tab to 3rd and Poof and so on
4. Basically all will then poof to main Meepo and Poof the victim to death

I think there is a guide on YouTube from a Pro player on how to practise with this

I do agree that Chen is harder then Meepo but FYI there are actually scripts that are quite available only to help you with the multi keystroke.

Basically these scripts assign hotkeys and you can use it in lieu to the TAB, Shift and Poof.

BTW there are also scripts for the Invoker as well. As even the great pros sometimes forget the combos but with these scripts. BAM.

one example of the Ultra Invoker combo: Eules, Sunstrike, Meteor, Deafening Blast, (the skill that freezes the hero with every hit) and the fire Elementals.