Simply put...you don't. At present the program does not support the I-cue accessory. I know because I have 5 of the ETC S4 Lustr+ LED fixtures that have a Rosco Iris and I-cue attached.
You can't attach however, on your plot, you can get them close to their position and assign them control however they will not operate as you want. The S4 fixture simply shoots the light past the I-cue in live playback mode.
I believe this is something that is being worked on however the reflection issue is something of a bear to create which is why you'll not see any mirrorballs in the library.
Maybe Vangelis will give us both an update on if/when this my be an operational feature :)