I checked out the Bushnell IR Monocular you mentioned , is it this unit ? <http://www.amazon.com/Bushnell-Equinox-Digital-Vision-Monocular/dp/B004I8Q9JQ>
If it is , duct taping a higher output IR illuminator to will give you problems IMHO.
An IR Designator like the pictured below would probably give you the bolt on solution you seem to be looking for.
I'm pretty sure I have seen this housing specified to work under a more civilised ambient temperature & still be water resistant. There are plenty of other housing designs that have an IR emitter inside of them with adjustable optics , that will give you a _minimum_ dot size of 22mm @ 30 meters , if you open up the aperture of this 1 Watt (or higher) IR designator or any of the other housing's pictured below that can all be bought with an IR Laser output you should have no problems lighting up the maximum distance that a Gen1 or Gen1+ Night vision monocular is limited to.
Other Housings (with a green output) That you should be able to buy that give out an IR output if you look around or upload the pictures in Googles Image searcher <http://images.google.com/>
I'm not associated with any of these manufacturers , I am doing my own work on building a suitable IR Designator so I can use a DSLR camera to film & photograph "stuff" at night using a 400 mm telephoto lens
Getting a quality factory built ~2 Watt IR Laser designator legally imported through Customs & into Australia can be done as I have the qualifications required to do so , but the pile of paperwork & applications to numerous government departments that I am required to fill out , makes building a unit from scratch a more practical & educational experience.
With any "specials" that I build , I always end up with exactly what I want & have a comprehensive understanding of how it works.....
JB