Can you make one-time payments to IRS to avoid underpayment without completing estimated tax forms?

[Snailkite]

My wife and I are salaried and pay most of our taxes in our paychecks. If we realize capital gains early in the year, can I just submit a payment to the IRS to cover the expected taxes? The last couple of years our withholding has been short, even after eliminating exemptions and adding a fixed amount to be taken out each pay period (new withholding system not working great for us!). So, I know any capital gains could risk us being short and getting a penalty. I'd like to just send in 20% of the gains and cover my bets, but don't want to complete estimated tax forms if I don't have to. Can this be done?

[ToddL99]

Use IRS Direct Pay or see Can I pay my taxes in TurboTax Easy Extension? 

And, if you think you'll run out of time, go to Can IRS extensions be e-filed? for help in filing an extension.