Not being able to apply loads along the member seems like a limitation of the software (without adding more nodes). If you can only apply loads at the nodes then the proper way to do this is to get the Fixed-End Reactions of the distributed load in terms of point loads AND MOMENTS.
Basically, imagine that your member that is subjected to the DL is fully fixed at each end and get the reactions. Then you switch the sign of the reactions and these are the loads you will need to apply at the nodes.
So consider the member below. I will use SkyCiv Structural 3D software to show how this works. In red we have the DL load and in black are the reactions at the fixed ends.
So we can apply those reactions (flipping the sign) to the actual structure now as you can see below:
And we can actually use the same structural analysis software to verify that this is in fact the correct way to convert the DL to its equivalent nodal loads:
So you'll notice that the reactions and displacements are identical between the models! Any minor differences are due to rounding of the reactions which were used as the loads. However, by modelling it with point loads and moments, the shear force and bending moment diagrams will only have the correct values at the nodes (not throughout the member obviously) due to the differences between the loads. 7
If you're only looking for displacement and reactions then it is fine to model it like this.
NOTE: The dimensions of this frame did not match yours, so these values do not apply to you - it was just a simple example. The member I used was 3m across and 1m high. The software used was SkyCiv Structural 3D. You can signup for a free account here. The free account can analyse structures with up to 5 members so your portal frame can easily be solved. Of course you won't need to worry about converting the DL to its equivalent nodal loads because the software can handle mid-member loads.
Hope that helps. 7