I'm sure someone out there should have been able to find a way, with or without mods, but I wouldn't really know.
In any case, I actually agree with this idea. Only having one aircraft forces the operator to invest more focus on it, which, pared with the time it takes to respawn, could actually do a good job at both improving the experience for the operator, but also force them to use the other tools at their disposal. Why would I care if an enemy jet is going to shoot down one of my UCAVs when the other is mere seconds away?
Any limitation to the 'UAV' part of the 'UAV Operator' would likely force the role to lean further towards getting out into the field, rather than sitting outside the AO, or even at base, changing it from an aggressive, self contained, fighting element to more of a supporting one. This would actually be a pretty neato idea for the infantry on the ground, and could, possibly, push the UAVOP to be more inclined to focus on where enemy infantry positions are, for both their and the friendly infantry's survival.
When I play UAVOP, I have found the second UCAV to be more of a bother than an asset anyway, usually sending it to circle side mission just in case I want to have a look over there for whatever reason. I imagine there are a lot of people that like having two, but it just gets in the way for me. The idea of the UAVOP leaning more towards recon than CAS, of which this change would encourage, is enticing as well.