For the time being you can use the following workaround:
CSS:
	<style>
		.RadButton input {
			width: 100% !important;
		}
	</style>
ASPX:
		<telerik:RadButton ID="rbACH" runat="server" ToggleType="Radio" ButtonType="StandardButton" GroupName="test" AutoPostBack="false" Text="eCheck" Width="200px">
			<ToggleStates>
				<telerik:RadButtonToggleState Text="eCheck" PrimaryIconCssClass="rbToggleRadioChecked" />
				<telerik:RadButtonToggleState Text="eCheck" PrimaryIconCssClass="rbToggleRadio" />
			</ToggleStates>
		</telerik:RadButton>
		<br />
		<br />

		<telerik:RadButton ID="btnToggle" runat="server" ToggleType="Radio" ButtonType="StandardButton" GroupName="StandardButton" Width="200px">
			<ToggleStates>
				<telerik:RadButtonToggleState Text="Checked" PrimaryIconCssClass="rbToggleRadio" />
				<telerik:RadButtonToggleState Text="UnChecked" PrimaryIconCssClass="rbToggleRadio" />
			</ToggleStates>
		</telerik:RadButton>