Yes a regular bicycle can be adapted as a draisine or a railbike as we call them (to use on abandoned railways with the tracks in place)?
California, USA is big into this sort of thing. There are more books on the subject than websites to be sure of.
Although there are so many styles of railbikes out there, it would be quite difficult to know what would fit your needs, but I am fairly confident this site will be able to help you: Bentley Railbike CONSTRUCTION PLANS.
I take it, that you are looking into something like this:
They offer Bentley Railbike CONSTRUCTION PLANS for sale and they look like they are detachable, but you should confirm this with this company via email, writing or by phone to verify your needs.
CONSTRUCTION PLANS include 6 pages of text with detailed construction sequence and parts list keyed to the drawings, plus 10 sheets of drawings with most parts rendered full scale.
Easy construction - no welding or complex machining.
Adjustable outrigger wheel height.
Detach outrigger with 3 pins - folds after removal.
Wheel guide lift lever.
This is a proprietary design, and a patent shall be applied for in the near future.
A LICENSE (plans included) to construct a railbike in accordance with these plans may be purchased for $25 (US DOLLARS).
A Railbike - LIST of Parts and Materials can be seen here.