Hmm this is indeed tricky, and I can't seem to come up with an elegant solution apart from just typing it in directly:

```
[[1,1,1,1,1],
[1,1,1,1,1],
[1,1,1,1,1],
[1,1,1,1,1],
[1,1,1,1,1]]
```

If you absolutely need to not use any Matrix Var's and don't wan't to go the long way, you might be able to use the Identity(#) function to generate a matrix and then use several other functions to modify it (unfortunately Fill() needs a matrix variable and not just a matrix). If you were able to use a matrix variable, you could always do

`Identity(5->[J]:Fill(1,[J]`