Detecting rising edges from two different inputs
So you can indeed use the !PRE and !CLR lines on a JK Flip-Flop such as the 74ACT109 that has those lines. No need for a clock to be present, although you will want to tie the clock line low. As seen in the truth table from the datasheet: 



See how the CLK line is a "don't-care" if either !PRE or !CLR are active (low). 
And so long as the CLK is low when they both return to HIGH then the outputs will retain their previous state. 

If you want even more warm-fuzzies take a look at the actual logic-diagram:


Here I've activated the !PRE line by bringing it LOW and you can see it propagates through the logic to hold the value. 

It's essential an SR latch, it's just easier to get buy a JK FLIP-FLOP with set and reset than it is to buy just an SR latch. 

And finally these chips are like $0.20 so definitely buy one and bread-board it up.