When we teach a dyslexic to remember facts and figures, we use multi-sensory teaching (sound, visual, touch, movement, even taste!), so a password can be remembered by associating each letter or number with a colour, or a picture, or the person drawing rooms and placing each letter/number in an appropriate room (sometimes it's easier to visualise something in a place).
We also use 'chunking'. For example, a password could be A6342B12; break it up in 'chunks' such as 'A6, 34, 2B 12' or 'A63, 42B, 12'. In the second example the 63 would be better said as sixty-three, and the 42 as forty-two; this is easier to visualise in your head as it is said. You can see numbers and lettes as a measurement, perhaps, or look at the relations of the numbers (6 is twice 3, 4 is twice 2). A relationship like that might not be there but there is usually some link that can be made and therefore the memory can cope better with it.
Any memory aid is always best devised (with help) by the dyslexic him/herself.
Dyslexics are often very imaginative, so are able to come up with ingenious ways of coping.