As to some of the options available:
The most common low-cost option would be a maintenance work platform (sometimes called a maintenance cage) attached to the forks of the lift truck. Though I don't particularly like these, they are acceptable for occasional use and cost less than $1,000 (US).
Since it in sounds like you don't need to work all that high, a good rolling ladder is also an approved option. Once again, I don't particularly like rolling ladders but they are fine for occasional use.
There is also portable scaffolding that can be set up quickly for occasional use. I believe you can even get scaffolding with castors so you can roll it from one area to another.
In addition, there are numerous hydraulic work platforms that you simply roll to the location then either manually pump or use an electric pump to raise you to the proper level. These are safe and can be operated by one person (unlike a work platform attached to a lift truck).
Then you have scissors lifts that come in all types of configurations. If you only need it occasionally you can rent them from just about any equipment rental operation or purchase a used one at a reasonable price.

Greg, since you are from Ohio, I would recommend that you contact the Ohio Bureau of Workers' Compensation and avail yourself of their free safety consulting services. Their industrial safety consultants can provide you with hazard assessment and control assistance. They should be able to provide you with a method for your task that is safe, practical, and OSHA compliant. You can contact them at ohiobwc.com.

1. Yes, was speaking of the overhead guard.
2. Apologize above, I meant neither another lift truck nor a working platform was available, not that they were available.
3.Wasn't looking for an excuse
4. I don't necessarily agree that there are a "lot of options" as far as feasible ones.
5. Any responses from someone in the lift truck industry?

I'm assuming you are talking about climbing onto the top of the lift truck (top of the operator protective guard). Though I'll admit I've done that once or twice, the fact is this is not an approved piece of equipment for that task and I don't see how incorporating fall protection is going to change that.

You really need to look at equipment designed specifically for the types of maintenance tasks you are doing. There are a lot of options, and many are relatively inexpensive including options to rent equipment for occasional use. The "we don't have the right equipment" excuse just doesn't fly.