Can I set a session parameter to a variable?

I have a tank of fluid of which I would like to control the temperature. I read a temperature from a thermocouple through a background analog input channel.

inputSession = daq.createSession('ni');
inputSession.DurationInSeconds = 1;
inputSession.Rate = 2;
inputSession.IsContinuous = 1;
inputSession.NotifyWhenDataAvailableExceeds = 2;
slot1 = addAnalogInputChannel(inputSession,'cDAQ3Mod1',0,'Thermocouple');
slot1(1).ThermocoupleType = 'T';
lh = addlistener(inputSession,'DataAvailable',@listenerFunction);
startBackground(inputSession);

The temperature can be controlled by sending a PWM signal to a heater. I control the heater by adjusting the 'DutyCycle' of a background counter output channel.

ctrSession = daq.createSession('ni');
ctrSession.IsContinuous = 1;
slot2 = addCounterOutputChannel(ctrSession,'cDAQ3Mod2',0,'PulseGeneration');
slot2.Frequency = 1;
ctrSession.Channels(1).DutyCycle = 0.2;
startBackground(ctrSession);

I would like to dynamically update the duty cycle of the background counter channel. I do this by performing calculations in the @listenerFunction. I also plot the temperature on a set of axes using the same @listenerFunction. When I try to update the the duty cycle directly from the @listenerFunction it causes terrible lag in the plot function.

Is there any way for me to set the duty cycle parameter of the channel to a variable (global or not)?

Thanks!