Use delayed_latch with a really short delay, like 2 ms. It will stay on until turned off by some other input. The latch delay would be too short to be performed on the input to turn off, so in effect, it is a force_on.
delayed_latch
When the input activates, the output will
activate. If the input is held active for longer than a period of time,
the output will latch on and stay on when the input deactivates. If
the input is held active for less than the time period, the output will
deactivate when the input deactivates. A previously latched output can
be turned off with a brief activation of the input or forced off by
another input. The default delay period is 1000ms. An optional
parameter allows the user to set the delay period in milliseconds. For
example, "delayed_latch 250" would latch after one quarter of a second.