Is there a way to secure an 18650 battery pack together without soldering, spot-welding, or an end cap kit?
Constructing battery packs without hard mechanical connections is usually a very bad idea.
Or worse.

In some cases the environment may not be hostile BUT an ebike is not such an environment.   40A is at least 10S2P for any 18650s.
(If you know of any manufacturer rated 40A discharge 18650s please point me to them - I'd be genuinely interested).

So &lt;= 20A / cell in 2P. Maybe 6.7A or 5A in 3P and 4P arrangements (deep ending on cells used). The odds of all those connections remaining good in an ebike environment is minimal. 

Spot welding / tabbing is cheap and easy.
A DIY spot welder is easy and cheap compared to all the other input required.   

Soldering is doable with fine bridge wires BUT a bad idea.
LiIon cells should not be soldered.
Fine wires plus luck skill and speed may allow you to 'get away with it'
Or not.



Soldering:

Soldering is a VERY bad idea - especially if you are not already skilled in the art of soldering.  Heating the end of a cell tends to break the electrical connection and heat elements of the interior that should not be heated. While some people report good results this is by no means certain. A "quick dab" to keep temperature rise low is a good way to create terrible joints. 



Spot welding:

There are numerous DIY spot welder descriptions on web.
This can be done using a battery as an energy source, either directly, or by adding a large capacitor.
A usually available method is to use a microwave over transformer.  Instructions are given in each case, but the basic method is to remove the high voltage secondary and add  a few turns of thick wire as low voltage secondary. Some people build elaborate mechanical electrode assemblies but something very simple indeed will suffice.

Here are many googlabet search links to DIY microwave transformer spot welders and  here are many images - each linked to a related page.