TL;DR No, you can't unless you modify a file. [Scroll to the Bottom!]
Here is me setting Smart Cast Spell 1,2,3, and 4 as Q,W,E, and R, respectively.
Now when I try to set Cast Spell 1,2,3,and 4 as [Shift]Q, [Shift]W, [Shift]E, and [Shift]R, this is the message I get. > Cast Spell ( ) cannot be bound as specified.
Key Bindings seems to only accept numbers and letters, in addition to some symbols.
So it seems there's actually a way to switch smartcast and normal cast. Found this from http://www.reddit.com/r/leagueoflegends/comments/o09bn/modify_smartcast_to_qwer_and_normal_cast_to/
Note: For this to work, you must have modified your key bindings in the past.
Go to C:\Riot Games\League of Legends\Config (Unless you have saved League of Legends in a different file)
Erase what you see in "Config" and paste in the following, without the space in between.
evtCastSpell1=[Shift][q]
evtCastSpell2=[Shift][w]
evtCastSpell3=[Shift][e]
evtCastSpell4=[Shift][r]
evtCastAvatarSpell1=[Shift][d]
evtCastAvatarSpell2=[Shift][f]
evtSmartCastSpell1=[q]
evtSmartCastSpell2=[w]
evtSmartCastSpell3=[e]
evtSmartCastSpell4=[r]
evtSmartCastAvatarSpell1=[d]
evtSmartCastAvatarSpell2=[f]
- Test it out in a custom game before heading to normals/ranked with your new settings. If you don't want to smartcast your 'AvatarSpells' or Summoner Spells, rather, don't paste in the last two lines.