You can make a one time deposit into your Wealthsimple account by choosing "Just this once" in the frequency section of the Move Funds page. 

How do I set one up?

From the website
1. Login to your Wealthsimple account
2. Click the 'Move funds' button
3. Select the bank account you would like to transfer funds out of
4. Select the Wealthsimple account you would like to transfer funds into
5. Enter the amount you'd like to transfer
6. Schedule the frequency of the transfer (if this a one-time contribution select "Just this once")
7. Choose a date for the transaction
8. Click 'Submit deposit' and you're done!