How to launch Technic from flashdrive

As Matt has suggested, you can use MultiMC as your custom launcher. It allows you to specify almost any variable when launching Minecraft, alongside mods.
In fact, to the point where you could run Technic (Minecraft) completely off your flash drive! (Provided it has the space to fit everything)

Disclaimer: All instructions presume you're using Windows, and not Mac/Lunix... And have Administrative privillages.
You can skip the Java installation step if the system you're playing on already has Java installed. ("Installing" Java is the only bit where you require Administrative privillages)

Step 1: Installing

1. You can install Java from the official download page.
2. Run the installer, but... Tick "Change Installation Directory". When prompted for a directory (in the installer), select one that's in your flash drive.
   Ensure that your Java installation is in its own seperate folder (just to keep things neat).
3. Download MultiMC onto your flash drive... And extract the .zip archive it comes in.

Step 2: Setting up an Minecraft Instance

1. On first-time launch (of MultiMC), it'll ask you to select a Java version. Simply browse to the installation on your flash disk and select it.
   It should be in: .../Java/jre8/bin/javaw.exe
2. Select "Accounts" on the top right-hand corner.
   Select "Manage Accounts" in the context menu. A window should pop up.
   In the dialogue, click "Add" and enter your login details.
   Ensure you have a connection to Mojang's login servers.

Note: You can repeat this section for as many mod packs as you would like to include. By 'mod packs', I also mean individual versions of Vanilla Minecraft.

3. Right click the center window and select "Create Instance" from the context menu.
4. Select the Minecraft version that Technic is currently running and name it as you wish.
   From memory, Technic is running 1.6.4.
5. Allow it to install Minecraft, or skip this step completely.

You should now find a new folder in: .../MultiMC/instances/<instance name>.
Alternatively, select the instance and click "Instance Folder" on the right-hand side pane.
At this stage, you can close MultiMC (if you want).

6. Open the new folder called minecraft and drag all the contents; files for your desired modpack into there.
   Technic files should be in: %Appdata%/.technic/modpacks/technic/....
   If there isn't already a minecraft folder in the instance folder, create one.
7. If any files needs to be replaced due to already existing, replace it!

Step 3: Playing

1. Open MultiMC (if it's not already open).
2. If a prompt comes up asking for the Java installation, select the one on your flash drive.
3. Play. (In offline mode if needed)
   Since you've already logged in, MultiMC simply uses your offline cached tokens.

From there, if any error occurs, you can disable mods from the "Instance Settings" window, and copy any logs from the secondary window that appears alongside Minecraft.

Multimc is probably the way forward here as it allows technic to be installed in a directory of your choosing without needing the .technic folder in %appdata%

Yes, but you would have to install technic to your flash drive, or you could move the .technic folder onto your flash drive. Then, you would have to set up a custom shortcut to your technic .exe in your .technic folder in your flash drive. After, you should just have to click on the technic shortcut to launch. Have not tried, will edit soon for answer to it working.