What to do with time gap before second Frozen Rain cast?

[Tiefman]

Often when I have decent haste (28% base + metranome, sephuz, icy veins, anything really) I can push for 3 frozen rain procs in the duration of one Frozen Orb. However, on the 2nd and 3rd cast of Freezing Rain there is 1 GCD of time before I can toss out the next blizzard. Casting another Frostbolt or Ice Lance delays it too much so I don't get a 3'rd FR cast. How should I manage this?

[Katsumi]

Get more or less haste? Maybe replace one IL cast in the middle with a Frostbolt?

[Aeliar]

I'll either just use Cone of Cold or Frost Nova+IL. I don't really expect more than 2 casts within Freezing Rain.