I'm hardly an expert at Construct, but it seems like the easiest workarounds for OR and ELSE would be:
For OR:
+ System: Always (every tick)
-> System: Set global variable 'Temp' to 0
+ System: Condition1 Equal to Condition2
-> System: Set global variable 'Temp' to 1
+ System: Condition1 Equal to Condition3
-> System: Set global variable 'Temp' to 1
+ System: Is global variable 'Temp' Equal to 1
-> (Do whatever)
For ELSE:
+ System: Condition1 Equal to Condition2
-> (Do whatever)
+ System: [negated] Condition1 Equal to Condition2
-> (Do whatever)
Not pretty, but workable. Note that this pseudo-ELSE doesn't work especially well if you change whatever you're testing against before you check against the negated bit. If that's the case, just set up a temporary variable and change it afterward.