How to charge a lipo battery inline with load
Yes, it is feasible. You just need to expose the balance plug and main positive and negative terminals (using a socket that cannot be accidentally shorted out or have something inappropriate plugged into it).

One possible problem is that the charger detects a full battery by monitoring the charge current and shutting off when it reaches 1/10th of the programmed current. At the standard charge rate of 4A the charger expects to shut off at ~400mA. However if your load is drawing 500mA then the charger may not properly detect the end of charge. While this won't damage the battery, the charger could run for longer than it needs to. Luckily your charger has a safety timer that can be set to 1-120 minutes (90 minutes should be plenty long enough).

You can charge through the balance connector by paralleling the positive and negative balance wires (red and black) with the main charger outputs. However the balance plug and wiring is only good for low current (&lt;2A) so the charging time will be longer.

Note that during charging the battery voltage will reach (or even slightly exceed) 8.4V for quite a long period of time. Make sure that your load can handle this.